Video encoding/decoding method and apparatus, and recording medium in which bit stream is stored

ABSTRACT

An image encoding/decoding method and apparatus are provided. An image decoding method performed by an image decoding apparatus of the present invention may comprise decoding an indicator indicating whether or not partition information of a current block is derived from partition information of a corresponding block of the current block, obtaining the partition information of the current block based on the decoded indicator, and partitioning the current block based on the obtained partition information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 16/342,310, filed on Apr. 16, 2019, which is a U.S.National Stage Application of International Application No.PCT/KR2017/011722, filed on Oct. 23, 2017, which claims the benefitunder 35 USC 119(a) and 365(b) of Korean Patent Application No.10-2016-0142274, filed on Oct. 28, 2016, in the Korean IntellectualProperty Office.

TECHNICAL FIELD

The present invention relates to a method and apparatus forencoding/decoding an image and a recording medium storing a bitstream.Particularly, the present invention relates to a method and apparatusfor encoding/decoding an image efficiently signaling block partitioninformation and a recording medium storing a bitstream generated by animage encoding method/apparatus of the present invention.

BACKGROUND ART

Recently, demands for high-resolution and high-quality images such ashigh definition (HD) images and ultra high definition (UHD) images, haveincreased in various application fields. However, higher resolution andquality image data has increasing amounts of data in comparison withconventional image data. Therefore, when transmitting image data byusing a medium such as conventional wired and wireless broadbandnetworks, or when storing image data by using a conventional storagemedium, costs of transmitting and storing increase. In order to solvethese problems occurring with an increase in resolution and quality ofimage data, high-efficiency image encoding/decoding techniques arerequired for higher-resolution and higher-quality images.

Image compression technology includes various techniques, including: aninter-prediction technique of predicting a pixel value included in acurrent picture from a previous or subsequent picture of the currentpicture; an intra-prediction technique of predicting a pixel valueincluded in a current picture by using pixel information in the currentpicture; a transform and quantization technique for compressing energyof a residual signal; an entropy encoding technique of assigning a shortcode to a value with a high appearance frequency and assigning a longcode to a value with a low appearance frequency; etc. Image data may beeffectively compressed by using such image compression technology, andmay be transmitted or stored.

DISCLOSURE Technical Problem

An object of the present invention is to provide a method and apparatusfor encoding/decoding an image to enhance compression efficiency.

Another object of the present invention is to provide a method andapparatus for encoding/decoding an image efficiently encoding/decodingpartition information of a block.

Another object of the present invention is to provide a method andapparatus for encoding/decoding an image efficiently signaling relevantinformation when partition information of a first block is derivablefrom partition information of a second block.

Another object of the present invention is to provide a recording mediumstoring a bitstream generated by an image encoding method or apparatusof the present invention.

Technical Solution

An image decoding method performed by an image decoding apparatusaccording to the present invention may comprise decoding an indicatorindicating whether or not partition information of a current block isderived from partition information of a corresponding block of thecurrent block, obtaining the partition information of the current blockbased on the decoded indicator, and partitioning the current block basedon the obtained partition information.

In the image decoding method of the present invention, the indicator maybe signaled in a CTU level or a picture level.

In the image decoding method of the present invention, when theindicator has a first value, the partition information of the currentblock may be obtained from the partition information of thecorresponding block, and when the indicator has a second value, thepartition information of the current block may be obtained by decodinginformation signaled through a bitstream.

In the image decoding method of the present invention, when thepartitioning of the current block includes first partitioning and secondpartitioning, the decoding of the indicator and the obtaining of thepartition information may be respectively performed for the firstpartitioning and the second partitioning.

In the image decoding method of the present invention, when thepartitioning of the current block includes first partitioning and secondpartitioning, the partition information of the current block for thefirst partitioning may be obtained from the partition information of thecorresponding block, and the partition information of the current blockfor the second partitioning may be obtained by decoding an indicator forthe second partitioning.

In the image decoding method of the present invention, when thepartitioning of the current block includes first partitioning and secondpartitioning, the indicator may indicate whether or not the partitioninformation of the current block is obtained from the partitioninformation of the corresponding block for both the first partitioningand the second partitioning, when the indicator has a first value, thepartition information of the current block may be obtained from thepartition information of the corresponding block for both the firstpartitioning and the second partitioning, and when the indicator has asecond value, the partition information of the current block may beobtained by decoding information signaled through a bitstream for boththe first partitioning and the second partitioning.

In the image decoding method of the present invention, the method mayfurther comprise comparing a size of the current block with apredetermined threshold value, and only when the size of the currentblock is greater than the predetermined threshold value, the decoding ofthe indicator may performed, and when the size of the current block isnot greater than the predetermined threshold value, the partitioninformation of the current block may be obtained by decoding informationsignaled through a bitstream.

In the image decoding method of the present invention, when thepartitioning of the current block includes first partitioning and secondpartitioning, the indicator for the first partitioning and the indicatorfor the second partitioning may be signaled in levels different fromeach other.

In the image decoding method of the present invention, the partitioninformation of the current block may include information about whetheror not partitioning is performed, and information of a partition form,and when the indicator indicates that the partition information of thecurrent block is derived from the partition information of thecorresponding block, one of the information about whether or notpartitioning is performed and the information of the partition form maybe derived from the partition information of the corresponding block,and the remaining one may be obtained by decoding information signaledthrough a bitstream.

In the image decoding method of the present invention, a partitionmethod of the current block may be determined based on at least one of acoding parameter, picture information, slice information, tileinformation, coding mode information, a quantization parameter (QP), acoding block flag (CBF), a block size, a block depth, a block form, anentropy encoding method, partition information of a neighbor block, anda temporal layer level.

In the image decoding method of the present invention, the current blockmay be a chroma block, and the corresponding block may be a luma blockcorresponding to the chroma block.

An image encoding method performed by an image encoding apparatusaccording to the present invention may comprises determining anindicator indicating whether or not partition information of a currentblock is derived from partition information of a corresponding block ofthe current block, obtaining the partition information of the currentblock based on the determined indicator, partitioning the current blockbased on the obtained partition information, and encoding at least oneof the indicator and the partition information of the current block.

In the image encoding method of the present invention, when theindicator has a first value, the partition information of the currentblock may not be encoded, and the indicator having the first value maybe encoded, and when the indicator has a second value, the indicatorhaving the second value and the partition information of the currentblock may be encoded.

In the image encoding method of the present invention, when thepartitioning of the current block includes first partitioning and secondpartitioning, the determining of the indicator, the obtaining of thepartition information, and the encoding of at least one of the indicatorand the partition information of the current block may be respectivelyperformed for the first partitioning and the second partitioning.

In the image encoding method of the present invention, when thepartitioning of the current block includes first partitioning and secondpartitioning, the partition information of the current block for thefirst partitioning may be obtained from the partition information of thecorresponding block, and both the indicator for the first partitioningand the partition information of the current block may not be encoded,and the partition information of the current block for the secondpartitioning may be obtained based on the indicator for the secondpartitioning, and the indicator having the first value may be encoded,or both the indicator having the second value and the partitioninformation of the current block may be encoded.

In the image encoding method of the present invention, when thepartitioning of the current block includes first partitioning and secondpartitioning, the indicator may indicate whether or not the partitioninformation of the current block for both the first partitioning and thesecond partitioning is derived from the partition information of thecorresponding block, when the indicator has a first value, the partitioninformation of the current block may not be encoded and the indicatorhaving the first value may be encoded for both the first partitioningand the second partitioning, and when the indicator has a second value,the indicator having the second value and the partition information ofthe current block may be encoded for both the first partitioning and thesecond partitioning.

In the image encoding method of the present invention, the method mayfurther comprise comparing a size of the current block with apredetermined threshold value, and only when the size of the currentblock is greater than the predetermined threshold value, the determiningof the indicator and the encoding of the indicator may be performed, andwhen the size of the current block is not greater than the predeterminedthreshold value, the partition information of the current block may beencoded.

A recording medium according to the present invention may store abitstream generated by an image encoding method.

Advantageous Effects

According to the present invention, a method and apparatus forencoding/decoding an image to enhance compression efficiency may beprovided.

According to the present invention, a method and apparatus forencoding/decoding an image efficiently encoding/decoding partitioninformation of a block may be provided.

According to the present invention, a method and apparatus forencoding/decoding an image efficiently signaling relevant informationwhen partition information of a first block is derivable from partitioninformation of a second block may be provided.

According to the present invention, a recording medium storing abitstream generated by an image encoding method or apparatus of thepresent invention may be provided.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing configurations of an encodingapparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram showing configurations of a decoding apparatusaccording to an embodiment of the present invention.

FIG. 3 is a view schematically showing a partition structure of an imagewhen encoding and decoding the image.

FIG. 4 is a view for explaining an embodiment of a process of intraprediction.

FIG. 5 is a view for explaining an embodiment of a process of interprediction.

FIG. 6 is a view for explaining a process of transformation andquantization.

FIG. 7 is a view for illustrating deriving of block partitioninformation in a CTU level.

FIGS. 8a and 8b illustrate operations corresponding to the example (a)shown in FIG. 7.

FIGS. 9a and 9b illustrate operations corresponding to the example (b)shown in FIG. 7.

FIGS. 10a and 10b illustrate operations corresponding to the example (c)shown in FIG. 7.

FIG. 11 is a view for illustrating deriving of block partitioninformation in a CU level.

FIGS. 12a and 12b illustrate operations corresponding to the example (a)shown in FIG. 11.

FIGS. 13a and 13b illustrate operations corresponding to the example (b)shown in FIG. 11.

FIGS. 14a and 14b illustrate operations corresponding to the example (c)shown in FIG. 11.

FIG. 15 is a view for illustrating deriving of block partitioninformation in a PPS level.

FIGS. 16a and 16b illustrate operations corresponding to the example (a)shown in FIG. 15.

FIGS. 17a and 17b illustrate operations corresponding to the example (b)shown in FIG. 15.

FIGS. 18a and 18b illustrate operations corresponding to the example (c)shown in FIG. 15.

FIGS. 19a and 19b illustrate operations corresponding to the example (d)shown in FIG. 15.

FIGS. 20a and 20b illustrate operations corresponding to the example (e)shown in FIG. 15.

FIGS. 21a and 21b illustrate operations corresponding to the example (f)shown in FIG. 15.

FIGS. 22a to 22d are views showing various types of block partitioning.

MODE FOR CARRYING OUT THE INVENTION

A variety of modifications may be made to the present invention andthere are various embodiments of the present invention, examples ofwhich will now be provided with reference to drawings and described indetail. However, the present invention is not limited thereto, althoughthe exemplary embodiments can be construed as including allmodifications, equivalents, or substitutes in a technical concept and atechnical scope of the present invention. The similar reference numeralsrefer to the same or similar functions in various aspects. In thedrawings, the shapes and dimensions of elements may be exaggerated forclarity. In the following detailed description of the present invention,references are made to the accompanying drawings that show, by way ofillustration, specific embodiments in which the invention may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to implement the present disclosure. Itshould be understood that various embodiments of the present disclosure,although different, are not necessarily mutually exclusive. For example,specific features, structures, and characteristics described herein, inconnection with one embodiment, may be implemented within otherembodiments without departing from the spirit and scope of the presentdisclosure. In addition, it should be understood that the location orarrangement of individual elements within each disclosed embodiment maybe modified without departing from the spirit and scope of the presentdisclosure. The following detailed description is, therefore, not to betaken in a limiting sense, and the scope of the present disclosure isdefined only by the appended claims, appropriately interpreted, alongwith the full range of equivalents to what the claims claim.

Terms used in the specification, ‘first’, ‘second’, etc. can be used todescribe various components, but the components are not to be construedas being limited to the terms. The terms are only used to differentiateone component from other components. For example, the ‘first’ componentmay be named the ‘second’ component without departing from the scope ofthe present invention, and the ‘second’ component may also be similarlynamed the ‘first’ component. The term ‘and/or’ includes a combination ofa plurality of items or any one of a plurality of terms.

It will be understood that when an element is simply referred to asbeing ‘connected to’ or ‘coupled to’ another element without being‘directly connected to’ or ‘directly coupled to’ another element in thepresent description, it may be ‘directly connected to’ or ‘directlycoupled to’ another element or be connected to or coupled to anotherelement, having the other element intervening therebetween. In contrast,it should be understood that when an element is referred to as being“directly coupled” or “directly connected” to another element, there areno intervening elements present.

Furthermore, constitutional parts shown in the embodiments of thepresent invention are independently shown so as to representcharacteristic functions different from each other. Thus, it does notmean that each constitutional part is constituted in a constitutionalunit of separated hardware or software. In other words, eachconstitutional part includes each of enumerated constitutional parts forconvenience. Thus, at least two constitutional parts of eachconstitutional part may be combined to form one constitutional part orone constitutional part may be divided into a plurality ofconstitutional parts to perform each function. The embodiment where eachconstitutional part is combined and the embodiment where oneconstitutional part is divided are also included in the scope of thepresent invention, if not departing from the essence of the presentinvention.

The terms used in the present specification are merely used to describeparticular embodiments, and are not intended to limit the presentinvention. An expression used in the singular encompasses the expressionof the plural, unless it has a clearly different meaning in the context.In the present specification, it is to be understood that terms such as“including”, “having”, etc. are intended to indicate the existence ofthe features, numbers, steps, actions, elements, parts, or combinationsthereof disclosed in the specification, and are not intended to precludethe possibility that one or more other features, numbers, steps,actions, elements, parts, or combinations thereof may exist or may beadded. In other words, when a specific element is referred to as being“included”, elements other than the corresponding element are notexcluded, but additional elements may be included in embodiments of thepresent invention or the scope of the present invention.

In addition, some of constituents may not be indispensable constituentsperforming essential functions of the present invention but be selectiveconstituents improving only performance thereof. The present inventionmay be implemented by including only the indispensable constitutionalparts for implementing the essence of the present invention except theconstituents used in improving performance. The structure including onlythe indispensable constituents except the selective constituents used inimproving only performance is also included in the scope of the presentinvention.

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. In describingexemplary embodiments of the present invention, well-known functions orconstructions will not be described in detail since they mayunnecessarily obscure the understanding of the present invention. Thesame constituent elements in the drawings are denoted by the samereference numerals, and a repeated description of the same elements willbe omitted.

In addition, hereinafter, an image may mean a picture configuring avideo, or may mean the video itself. For example, “encoding or decodingor both of an image” may mean “encoding or decoding or both of a video”,and may mean “encoding or decoding or both of one image among images ofa video.” Here, a picture and the image may have the same meaning.

Description of Terms

Encoder: means an apparatus performing encoding.

Decoder: means an apparatus performing decoding

Block: is an M×N array of a sample. Herein, M and N mean positiveintegers, and the block may mean a sample array of a two-dimensionalform. The block may refer to a unit. A current block my mean an encodingtarget block that becomes a target when encoding, or a decoding targetblock that becomes a target when decoding. In addition, the currentblock may be at least one of an encode block, a prediction block, aresidual block, and a transform block.

Sample: is a basic unit constituting a block. It may be expressed as avalue from 0 to 2^(Bd)−1 according to a bit depth (B_(d)). In thepresent invention, the sample may be used as a meaning of a pixel.

Unit: refers to an encoding and decoding unit. When encoding anddecoding an image, the unit may be a region generated by partitioning asingle image. In addition, the unit may mean a subdivided unit when asingle image is partitioned into subdivided units during encoding ordecoding. When encoding and decoding an image, a predetermined processfor each unit may be performed. A single unit may be partitioned intosub-units that have sizes smaller than the size of the unit. Dependingon functions, the unit may mean a block, a macroblock, a coding treeunit, a code tree block, a coding unit, a coding block), a predictionunit, a prediction block, a residual unit), a residual block, atransform unit, a transform block, etc. In addition, in order todistinguish a unit from a block, the unit may include a luma componentblock, a chroma component block associated with the luma componentblock, and a syntax element of each color component block. The unit mayhave various sizes and forms, and particularly, the form of the unit maybe a two-dimensional geometrical figure such as a rectangular shape, asquare shape, a trapezoid shape, a triangular shape, a pentagonal shape,etc. In addition, unit information may include at least one of a unittype indicating the coding unit, the prediction unit, the transformunit, etc., and a unit size, a unit depth, a sequence of encoding anddecoding of a unit, etc.

Coding Tree Unit: is configured with a single coding tree block of aluma component Y, and two coding tree blocks related to chromacomponents Cb and Cr. In addition, it may mean that including the blocksand a syntax element of each block. Each coding tree unit may bepartitioned by using at least one of a quad-tree partitioning method anda binary-tree partitioning method to configure a lower unit such ascoding unit, prediction unit, transform unit, etc. It may be used as aterm for designating a pixel block that becomes a process unit whenencoding/decoding an image as an input image.

Coding Tree Block: may be used as a term for designating any one of a Ycoding tree block, Cb coding tree block, and Cr coding tree block.

Neighbor Block: means a block adjacent to a current block. The blockadjacent to the current block may mean a block that comes into contactwith a boundary of the current block, or a block positioned within apredetermined distance from the current block. The neighbor block maymean a block adjacent to a vertex of the current block. Herein, theblock adjacent to the vertex of the current block may mean a blockvertically adjacent to a neighbor block that is horizontally adjacent tothe current block, or a block horizontally adjacent to a neighbor blockthat is vertically adjacent to the current block.

Reconstructed Neighbor block: means a neighbor block adjacent to acurrent block and which has been already spatially/temporally encoded ordecoded. Herein, the reconstructed neighbor block may mean areconstructed neighbor unit. A reconstructed spatial neighbor block maybe a block within a current picture and which has been alreadyreconstructed through encoding or decoding or both. A reconstructedtemporal neighbor block is a block at the same position as the currentblock of the current picture within a reference picture, or a neighborblock thereof.

Unit Depth: means a partitioned degree of a unit. In a tree structure, aroot node may be the highest node, and a leaf node may be the lowestnode. In addition, when a unit is expressed as a tree structure, a levelin which a unit is present may mean a unit depth.

Bitstream: means a bitstream including encoding image information.

Parameter Set: corresponds to header information among a configurationwithin a bitstream. At least one of a video parameter set, a sequenceparameter set, a picture parameter set, and an adaptation parameter setmay be included in a parameter set. In addition, a parameter set mayinclude a slice header, and tile header information.

Parsing: may mean determination of a value of a syntax element byperforming entropy decoding, or may mean the entropy decoding itself.

Symbol: may mean at least one of a syntax element, a coding parameter,and a transform coefficient value of an encoding/decoding target unit.In addition, the symbol may mean an entropy encoding target or anentropy decoding result.

Prediction Unit: means a basic unit when performing prediction such asinter-prediction, intra-prediction, inter-compensation,intra-compensation, and motion compensation. A single prediction unitmay be partitioned into a plurality of partitions with a small size, ormay be partitioned into a lower prediction unit.

Prediction Unit Partition: means a form obtained by partitioning aprediction unit.

Reference Picture List: means a list including one or more referencepictures used for inter-picture prediction or motion compensation. LC(List Combined), L0 (List 0), L1 (List 1), L2 (List 2), L3 (List 3) andthe like are types of reference picture lists. One or more referencepicture lists may be used for inter-picture prediction.

Inter-picture prediction Indicator: may mean an inter-picture predictiondirection (uni-directional prediction, bi-directional prediction, andthe like) of a current block. Alternatively, the inter-pictureprediction indicator may mean the number of reference pictures used togenerate a prediction block of a current block. Further alternatively,the inter-picture prediction indicator may mean the number of predictionblocks used to perform inter-picture prediction or motion compensationwith respect to a current block.

Reference Picture Index: means an index indicating a specific referencepicture in a reference picture list.

Reference Picture: may mean a picture to which a specific block refersfor inter-picture prediction or motion compensation.

Motion Vector: is a two-dimensional vector used for inter-pictureprediction or motion compensation and may mean an offset between areference picture and an encoding/decoding target picture. For example,(mvX, mvY) may represent a motion vector, mvX may represent a horizontalcomponent, and mvY may represent a vertical component.

Motion Vector Candidate: may mean a block that becomes a predictioncandidate when predicting a motion vector, or a motion vector of theblock. A motion vector candidate may be listed in a motion vectorcandidate list.

Motion Vector Candidate List: may mean a list of motion vectorcandidates.

Motion Vector Candidate Index: means an indicator indicating a motionvector candidate in a motion vector candidate list. It is also referredto as an index of a motion vector predictor.

Motion Information: may mean information including a motion vector, areference picture index, an inter-picture prediction indicator, and atleast any one among reference picture list information, a referencepicture, a motion vector candidate, a motion vector candidate index, amerge candidate, and a merge index.

Merge Candidate List: means a list composed of merge candidates.

Merge Candidate: means a spatial merge candidate, a temporal mergecandidate, a combined merge candidate, a combined bi-prediction mergecandidate, a zero merge candidate, or the like. The merge candidate mayhave an inter-picture prediction indicator, a reference picture indexfor each list, and motion information such as a motion vector.

Merge Index: means information indicating a merge candidate within amerge candidate list. The merge index may indicate a block used toderive a merge candidate, among reconstructed blocks spatially and/ortemporally adjacent to a current block. The merge index may indicate atleast one item in the motion information possessed by a merge candidate.

Transform Unit: means a basic unit used when encoding or decoding aresidual signal, for example, when performing transform, reversetransform, quantization, dequantization, or transform coefficientencoding/decoding. One transform unit may be partitioned into aplurality of smaller transform units.

Scaling: means a process of multiplying a transform coefficient level bya factor. A transform coefficient may be generated by scaling atransform coefficient level. The scaling also may be referred to asdequantization.

Quantization Parameter: may mean a value used when generating atransform coefficient level of a transform coefficient duringquantization. The quantization parameter also may mean a value used whengenerating a transform coefficient by scaling a transform coefficientlevel during dequantization. The quantization parameter may be a valuemapped on a quantization step size.

Delta Quantization Parameter: means a difference value between apredicted quantization parameter and a quantization parameter of anencoding/decoding target unit.

Scan: means a method of sequencing coefficients within a block or amatrix. For example, changing a two-dimensional matrix of coefficientsinto a one-dimensional matrix may be referred to as scanning, andchanging a one-dimensional matrix of coefficients into a two-dimensionalmatrix may be referred to as scanning or inverse scanning.

Transform Coefficient: may mean a coefficient value generated aftertransform is performed in an encoder. It may mean a coefficient valuegenerated after at least one of entropy decoding and dequantization isperformed in a decoder. A quantized level obtained by quantizing atransform coefficient or a residual signal, or a quantized transformcoefficient level also may fall within the meaning of the transformcoefficient.

Quantized Level: means a value generated by quantizing a transformcoefficient or a residual signal in an encoder. Alternatively, thequantized level may mean a value that is a dequantization target toundergo dequantization in a decoder. Similarly, a quantized transformcoefficient level that is a result of transform and quantization alsomay fall within the meaning of the quantized level.

Non-zero Transform Coefficient: means a transform coefficient having avalue other than zero, or a transform coefficient level having a valueother than zero.

Quantization Matrix: means a matrix used in a quantization process or adequantization process performed to improve subjective or objectiveimage quality. The quantization matrix also may be referred to as ascaling list.

Quantization Matrix Coefficient: means each element within aquantization matrix. The quantization matrix coefficient also may bereferred to as a matrix coefficient.

Default Matrix: means a predetermined quantization matrix preliminarilydefined in an encoder or a decoder.

Non-default Matrix: means a quantization matrix that is notpreliminarily defined in an encoder or a decoder but is signaled by auser.

FIG. 1 is a block diagram illustrating the construction of an encodingapparatus according to one embodiment of the present invention.

An encoding apparatus 100 may be an encoder, a video encoding apparatus,or an image encoding apparatus. A video may include one or more images(or pictures). The encoding apparatus 100 can sequentially encode one ormore pictures.

With reference to FIG. 1, the encoding apparatus 100 includes a motionprediction unit 111, a motion compensation unit 112, an intra-predictionunit 120, a switch 115, a subtractor 125, a transform unit 130, aquantization unit 140, an entropy encoding unit 150, a dequantizationunit 160, a reverse-transform unit 170, an adder 175, a filter unit 180,and a reference picture buffer 190.

The encoding apparatus 100 can perform encoding on an input pictureusing an intra mode and/or an inter mode. The encoding apparatus 100 maygenerate a bitstream by encoding an input picture and output thegenerated bitstream. The generated bitstream may be recorded on acomputer-readable recording medium or streamed via a wired or wirelesstransmission medium. When an intra mode is used as a prediction mode,the switch 115 may be switched to intra. Meanwhile, when an inter modeis used as a prediction mode, the switch 115 may be switched to inter.Here, the intra mode may mean an intra-picture prediction mode, and theinter mode may mean an inter-picture prediction mode. The encodingapparatus 100 may generate a prediction block of an input block of aninput picture. After the prediction block is generated, the encodingapparatus 100 may encode a residual between the input block and theprediction block. The input picture can be referred to as a currentpicture that is an encoding target picture to undergo current encoding.The input block can be referred to as a current block or an encodingtarget block to undergo current encoding.

When the prediction mode is the intra mode, the intra-prediction unit120 may use a pixel value of a neighboring block that has been alreadyencoded or decoded as a reference pixel. The intra-prediction unit 120may perform spatial prediction on the input block by using the referencepixel, and generate prediction samples of the input block through thespatial prediction. Here, the intra-prediction may mean intra-pictureprediction.

When the prediction mode is the inter mode, the motion prediction unit111 may search a reference picture for a region that best matches theinput block during a motion prediction process, and derive a motionvector using the searched region. The reference picture may be stored inthe reference picture buffer 190.

The motion compensation unit 112 may generate a prediction block byperforming motion compensation using a motion vector. Here, theinter-prediction may mean inter-picture prediction or motioncompensation.

When the value of the motion vector is not an integer, the motionprediction unit 111 and the motion compensation unit 112 may generatethe prediction block by applying an interpolation filter to a partialregion of the reference picture. In order to perform inter-pictureprediction or motion compensation on a coding unit, it may be determinedthat which mode among a skip mode, a merge mode, an advanced motionvector prediction (AMVP) mode, and a current picture referring mode isused for motion prediction and motion compensation of a prediction unitincluded in the corresponding coding unit. Then, inter-pictureprediction or motion compensation may be differently performed dependingon the determined mode.

The subtractor 125 may generate a residual block by using a residual ofan input block and a prediction block. The residual block may be calledas a residual signal. The residual signal may mean a difference betweenan original signal and a prediction signal. In addition, the residualsignal may be a signal generated by transforming or quantizing, ortransforming and quantizing a difference between the original signal andthe prediction signal. The residual block may be a residual signal of ablock unit.

The transform unit 130 may generate a transform coefficient byperforming transform of a residual block, and output the generatedtransform coefficient. Herein, the transform coefficient may be acoefficient value generated by performing transform of the residualblock. When a transform skip mode is applied, the transform unit 130 mayskip transform of the residual block.

A quantized level may be generated by applying quantization to thetransform coefficient or to the residual signal. Hereinafter, thequantized level may be also called as a transform coefficient inembodiments.

The quantization unit 140 may generate a quantized level by quantizingthe transform coefficient or the residual signal according to aparameter, and output the generated quantized level. Herein, thequantization unit 140 may quantize the transform coefficient by using aquantization matrix.

The entropy encoding unit 150 may generate a bitstream by performingentropy encoding according to a probability distribution on valuescalculated by the quantization unit 140 or on coding parameter valuescalculated when performing encoding, and output the generated bitstream.The entropy encoding unit 150 may perform entropy encoding of pixelinformation of an image and information for decoding an image. Forexample, the information for decoding the image may include a syntaxelement.

When entropy encoding is applied, symbols are represented so that asmaller number of bits are assigned to a symbol having a high chance ofbeing generated and a larger number of bits are assigned to a symbolhaving a low chance of being generated, and thus, the size of bit streamfor symbols to be encoded may be decreased. The entropy encoding unit150 may use an encoding method for entropy encoding such as exponentialGolomb, context-adaptive variable length coding (CAVLC),context-adaptive binary arithmetic coding (CABAC), etc. For example, theentropy encoding unit 150 may perform entropy encoding by using avariable length coding/code (VLC) table. In addition, the entropyencoding unit 150 may deduce a binarization method of a target symboland a probability model of a target symbol/bin, and perform arithmeticcoding by using the deduced binarization method, and a context model.

In order to encode a transform coefficient level, the entropy encodingunit 150 may change a two-dimensional block form coefficient into aone-dimensional vector form by using a transform coefficient scanningmethod.

A coding parameter may include information (flag, index, etc.) such assyntax element that is encoded in an encoder and signaled to a decoder,and information derived when performing encoding or decoding. The codingparameter may mean information required when encoding or decoding animage. For example, at least one value or a combination form of aunit/block size, a unit/block depth, unit/block partition information,unit/block partition structure, whether to partition of a quad-treeform, whether to partition of a binary-tree form, a partition directionof a binary-tree form (horizontal direction or vertical direction), apartition form of a binary-tree form (symmetric partition or asymmetricpartition), an intra-prediction mode/direction, a reference samplefiltering method, a prediction block filtering method, a predictionblock filter tap, a prediction block filter coefficient, aninter-prediction mode, motion information, a motion vector, a referencepicture index, a inter-prediction angle, an inter-prediction indicator,a reference picture list, a reference picture, a motion vector predictorcandidate, a motion vector candidate list, whether to use a merge mode,a merge candidate, a merge candidate list, whether to use a skip mode,an interpolation filter type, an interpolation filter tab, aninterpolation filter coefficient, a motion vector size, a presentationaccuracy of a motion vector, a transform type, a transform size,information of whether or not a primary (first) transform is used,information of whether or not a secondary transform is used, a primarytransform index, a secondary transform index, information of whether ornot a residual signal is present, a coded block pattern, a coded blockflag (CBF), a quantization parameter, a quantization matrix, whether toapply an intra loop filter, an intra loop filter coefficient, an intraloop filter tab, an intra loop filter shape/form, whether to apply adeblocking filter, a deblocking filter coefficient, a deblocking filtertab, a deblocking filter strength, a deblocking filter shape/form,whether to apply an adaptive sample offset, an adaptive sample offsetvalue, an adaptive sample offset category, an adaptive sample offsettype, whether to apply an adaptive in-loop filter, an adaptive in-loopfilter coefficient, an adaptive in-loop filter tab, an adaptive in-loopfilter shape/form, a binarization/inverse-binarization method, a contextmodel determining method, a context model updating method, whether toperform a regular mode, whether to perform a bypass mode, a context bin,a bypass bin, a transform coefficient, a transform coefficient level, atransform coefficient level scanning method, an imagedisplaying/outputting sequence, slice identification information, aslice type, slice partition information, tile identificationinformation, a tile type, tile partition information, a picture type, abit depth, and information of a luma signal or chroma signal may beincluded in the coding parameter.

Herein, signaling the flag or index may mean that a corresponding flagor index is entropy encoded and included in a bitstream by an encoder,and may mean that the corresponding flag or index is entropy decodedfrom a bitstream by a decoder.

When the encoding apparatus 100 performs encoding throughinter-prediction, an encoded current image may be used as a referenceimage for another image that is processed afterwards. Accordingly, theencoding apparatus 100 may reconstruct or decode the encoded currentimage, or store the reconstructed or decoded image as a reference image.

A quantized level may be dequantized in the dequantization unit 160, ormay be inverse-transformed in the inverse-transform unit 170. Adequantized or inverse-transformed coefficient or both may be added witha prediction block by the adder 175. By adding the dequantized orinverse-transformed coefficient or both with the prediction block, areconstructed block may be generated. Herein, the dequantized orinverse-transformed coefficient or both may mean a coefficient on whichat least one of dequantization and inverse-transform is performed, andmay mean a reconstructed residual block.

A reconstructed block may pass through the filter unit 180. The filterunit 180 may apply at least one of a deblocking filter, a sampleadaptive offset (SAO), and an adaptive loop filter (ALF) to thereconstructed block or a reconstructed image. The filter unit 180 may becalled as an in-loop filter.

The deblocking filter may remove block distortion generated inboundaries between blocks. In order to determine whether or not to applya deblocking filter, whether or not to apply a deblocking filter to acurrent block may be determined based pixels included in several rows orcolumns which are included in the block. When a deblocking filter isapplied to a block, another filter may be applied according to arequired deblocking filtering strength.

In order to compensate an encoding error, a proper offset value may beadded to a pixel value by using a sample adaptive offset. The sampleadaptive offset may correct an offset of a deblocked image from anoriginal image by a pixel unit. A method of partitioning pixels of animage into a predetermined number of regions, determining a region towhich an offset is applied, and applying the offset to the determinedregion, or a method of applying an offset in consideration of edgeinformation on each pixel may be used.

The adaptive loop filter may perform filtering based on a comparisonresult of the filtered reconstructed image and the original image.Pixels included in an image may be partitioned into predeterminedgroups, a filter to be applied to each group may be determined, anddifferential filtering may be performed for each group. Information ofwhether or not to apply the ALF may be signaled by coding units (CUs),and a form and coefficient of the ALF to be applied to each block mayvary.

The reconstructed block or the reconstructed image having passed throughthe filter unit 180 may be stored in the reference picture buffer 190.FIG. 2 is a block diagram showing a configuration of a decodingapparatus according to an embodiment and to which the present inventionis applied.

A decoding apparatus 200 may a decoder, a video decoding apparatus, oran image decoding apparatus.

Referring to FIG. 2, the decoding apparatus 200 may include an entropydecoding unit 210, a dequantization unit 220, a inverse-transform unit230, an intra-prediction unit 240, a motion compensation unit 250, anadder 225, a filter unit 260, and a reference picture buffer 270.

The decoding apparatus 200 may receive a bitstream output from theencoding apparatus 100. The decoding apparatus 200 may receive abitstream stored in a computer readable recording medium, or may receivea bitstream that is streamed through a wired/wireless transmissionmedium. The decoding apparatus 200 may decode the bitstream by using anintra mode or an inter mode. In addition, the decoding apparatus 200 maygenerate a reconstructed image generated through decoding or a decodedimage, and output the reconstructed image or decoded image.

When a prediction mode used when decoding is an intra mode, a switch maybe switched to an intra. Alternatively, when a prediction mode used whendecoding is an inter mode, a switch may be switched to an inter mode.

The decoding apparatus 200 may obtain a reconstructed residual block bydecoding the input bitstream, and generate a prediction block. When thereconstructed residual block and the prediction block are obtained, thedecoding apparatus 200 may generate a reconstructed block that becomes adecoding target by adding the reconstructed residual block with theprediction block. The decoding target block may be called a currentblock.

The entropy decoding unit 210 may generate symbols by entropy decodingthe bitstream according to a probability distribution. The generatedsymbols may include a symbol of a quantized level form. Herein, anentropy decoding method may be a inverse-process of the entropy encodingmethod described above.

In order to decode a transform coefficient level, the entropy decodingunit 210 may change a one-directional vector form coefficient into atwo-dimensional block form by using a transform coefficient scanningmethod.

A quantized level may be dequantized in the dequantization unit 220, orinverse-transformed in the inverse-transform unit 230. The quantizedlevel may be a result of dequantizing or inverse-transforming or both,and may be generated as a reconstructed residual block. Herein, thedequantization unit 220 may apply a quantization matrix to the quantizedlevel.

When an intra mode is used, the intra-prediction unit 240 may generate aprediction block by performing spatial prediction that uses a pixelvalue of a block adjacent to a decoding target block and which has beenalready decoded.

When the inter mode is used, the motion compensation unit 250 maygenerate a prediction block by performing motion compensation using boththe motion vector and the reference picture stored in the referencepicture buffer 270. When the value of the motion vector is not aninteger, the motion compensation unit 250 may generate the predictionblock by applying the interpolation filter to a partial region of areference picture. In order to perform motion compensation on a codingunit, it may be first determined that which mode among a skip mode, amerge mode, an AMVP mode, and a current picture reference mode is to beused for motion compensation of a prediction unit included in thecorresponding coding unit, and the motion compensation may then beperformed according to the determined mode.

The adder 225 may generate a reconstructed block by adding thereconstructed residual block with the prediction block. The filter unit260 may apply at least one of a deblocking filter, a sample adaptiveoffset, and an adaptive loop filter to the reconstructed block orreconstructed image. The filter unit 260 may output the reconstructedimage. The reconstructed block or reconstructed image may be stored inthe reference picture buffer 270 and used when performinginter-prediction.

FIG. 3 is a view schematically showing a partition structure of an imagewhen encoding and decoding the image. FIG. 3 schematically shows anexample of partitioning a single unit into a plurality of lower units.

In order to efficiently partition an image, when encoding and decoding,a coding unit (CU) may be used. The coding unit may be used as a basicunit when encoding/decoding the image. In addition, the coding unit maybe used as a unit for distinguishing an intra mode and an inter modewhen encoding/decoding the image. The coding unit may be a basic unitused for prediction, transform, quantization, inverse-transform,dequantization, or an encoding/decoding process of a transformcoefficient.

Referring to FIG. 3, an image 300 is sequentially partitioned in alargest coding unit (LCU), and a LCU unit is determined as a partitionstructure. Herein, the LCU may be used in the same meaning as a codingtree unit (CTU). A unit partitioning may mean partitioning a blockassociated with to the unit. In block partition information, informationof a unit depth may be included. Depth information may represent anumber of times or a degree or both in which a unit is partitioned. Asingle unit may be partitioned in a layer associated with depthinformation based on a tree structure. Each of partitioned lower unitmay have depth information. Depth information may be informationrepresenting a size of a CU, and may be stored in each CU.

A partition structure may mean a distribution of a coding unit (CU)within an LCU 310. Such a distribution may be determined according towhether or not to partition a single CU into a plurality (positiveinteger equal to or greater than 2 including 2, 4, 8, 16, etc.) of CUs.A horizontal size and a vertical size of the CU generated bypartitioning may respectively be half of a horizontal size and avertical size of the CU before partitioning, or may respectively havesizes smaller than a horizontal size and a vertical size beforepartitioning according to a number of times of partitioning. The CU maybe recursively partitioned into a plurality of CUs. Partitioning of theCU may be recursively performed until to a predefined depth orpredefined size. For example, a depth of an LCU may be 0, and a depth ofa smallest coding unit (SCU) may be a predefined maximum depth. Herein,the LCU may be a coding unit having a maximum coding unit size, and theSCU may be a coding unit having a minimum coding unit size as describedabove. Partitioning is started from the LCU 310, a CU depth increases by1 as a horizontal size or a vertical size or both of the CU decreases bypartitioning.

In addition, information whether or not the CU is partitioned may berepresented by using partition information of the CU. The partitioninformation may be 1-bit information. All CUs, except for a SCU, mayinclude partition information. For example, when a value of partitioninformation is 1, the CU may not be partitioned, when a value ofpartition information is 2, the CU may be partitioned.

Referring to FIG. 3, an LCU having a depth 0 may be a 64×64 block. 0 maybe a minimum depth. A SCU having a depth 3 may be an 8×8 block. 3 may bea maximum depth. A CU of a 32×32 block and a 16×16 block may berespectively represented as a depth 1 and a depth 2.

For example, when a single coding unit is partitioned into four codingunits, a horizontal size and a vertical size of the four partitionedcoding units may be a half size of a horizontal and vertical size of theCU before being partitioned. In one embodiment, when a coding unithaving a 32×32 size is partitioned into four coding units, each of thefour partitioned coding units may have a 16×16 size. When a singlecoding unit is partitioned into four coding units, it may be called thatthe coding unit may be partitioned into a quad-tree form.

For example, when a single coding unit is partitioned into two codingunits, a horizontal or vertical size of the two coding units may be ahalf of a horizontal or vertical size of the coding unit before beingpartitioned. For example, when a coding unit having a 32×32 size ispartitioned in a vertical direction, each of two partitioned codingunits may have a size of 16×32. When a single coding unit is partitionedinto two coding units, it may be called that the coding unit ispartitioned in a binary-tree form. An LCU 320 of FIG. 3 is an example ofan LCU to which both of partitioning of a quad-tree form andpartitioning of a binary-tree form are applied.

FIG. 4 is a view showing an intra-prediction process.

An intra-prediction mode may be a non-angular mode or an angular mode.The non-angular mode may be a DC mode or a planar mode, and the angularmode may be a prediction mode having a specific direction or angle. Theintra-prediction mode may be expressed by at least one of a mode number,a mode value, a mode numeral, and a mode angle. A number ofintra-prediction modes may be M including 1, and the non-angular and theangular mode.

A number of intra-prediction modes may be fixed to N regardless of ablock size. Alternatively, a number of intra-prediction modes may varyaccording to a block size or a color component type or both. Forexample, as a block size becomes large, a number of intra-predictionmodes may increase. Alternatively, a number of intra-prediction modes ofa luma component block may be larger than a number of intra-predictionmodes of a chroma component block.

In order to intra-predict a current block, a step of determining whetheror not samples included in a reconstructed neighbor block may be used asreference samples of the current block may be performed. When a samplethat is not usable as a reference sample of the current block ispresent, a value obtained by duplicating or performing interpolation onat least one sample value among samples included in the reconstructedneighbor block or both may be used to replace with a non-usable samplevalue of a sample, thus the replaced sample value is used as a referencesample of the current block.

When intra-predicting, a filter may be applied to at least one of areference sample and a prediction sample based on an intra-predictionmode and a current block size.

In case of a planar mode, when generating a prediction block of acurrent block, according to a position of a prediction target samplewithin a prediction block, a sample value of the prediction targetsample may be generated by using a weighted sum of an upper and leftside reference sample of a current sample, and a right upper side andleft lower side reference sample of the current block. In addition, incase of a DC mode, when generating a prediction block of a currentblock, an average value of upper side and left side reference samples ofthe current block may be used. In addition, in case of an angular mode,a prediction block may be generated by using an upper side, a left side,a right upper side, and/or a left lower side reference sample of thecurrent block. In order to generate a prediction sample value,interpolation of a real number unit may be performed.

An intra-prediction mode of a current block may be entropyencoded/decoded by predicting an intra-prediction mode of a blockpresent adjacent to the current block. When intra-prediction modes ofthe current block and the neighbor block are identical, information thatthe intra-prediction modes of the current block and the neighbor blockare identical may be signaled by using predetermined flag information.In addition, indicator information of an intra-prediction mode that isidentical to the intra-prediction mode of the current block amongintra-prediction modes of a plurality of neighbor blocks may besignaled. When intra-prediction modes of the current block and theneighbor block are different, intra-prediction mode information of thecurrent block may be entropy encoded/decoded by performing entropyencoding/decoding based on the intra-prediction mode of the neighborblock.

FIG. 5 is a diagram illustrating an embodiment of an inter-pictureprediction process.

In FIG. 5, a rectangle may represent a picture. In FIG. 5, an arrowrepresents a prediction direction. Pictures may be categorized intointra pictures (I pictures), predictive pictures (P pictures), andBi-predictive pictures (B pictures) according to the encoding typethereof.

The I picture may be encoded through intra-prediction without requiringinter-picture prediction. The P picture may be encoded throughinter-picture prediction by using a reference picture that is present inone direction (i.e., forward direction or backward direction) withrespect to a current block. The B picture may be encoded throughinter-picture prediction by using reference pictures that are preset intwo directions (i.e., forward direction and backward direction) withrespect to a current block. When the inter-picture prediction is used,the encoder may perform inter-picture prediction or motion compensationand the decoder may perform the corresponding motion compensation.

Hereinbelow, an embodiment of the inter-picture prediction will bedescribed in detail.

The inter-picture prediction or motion compensation may be performedusing a reference picture and motion information.

Motion information of a current block may be derived duringinter-picture prediction by each of the encoding apparatus 100 and thedecoding apparatus 200. The motion information of the current block maybe derived by using motion information of a reconstructed neighboringblock, motion information of a collocated block (also referred to as acol block or a co-located block), and/or a block adjacent to theco-located block. The co-located block may mean a block that is locatedspatially at the same position as the current block, within a previouslyreconstructed collocated picture (also referred to as a col picture or aco-located picture). The co-located picture may be one picture among oneor more reference pictures included in a reference picture list.

A method of deriving the motion information of the current block mayvary depending on a prediction mode of the current block. For example,as prediction modes for inter-picture prediction, there may be an AMVPmode, a merge mode, a skip mode, a current picture reference mode, etc.The merge mode may be referred to as a motion merge mode.

For example, when the AMVP is used as the prediction mode, at least oneof motion vectors of the reconstructed neighboring blocks, motionvectors of the co-located blocks, motion vectors of blocks adjacent tothe co-located blocks, and a (0, 0) motion vector may be determined asmotion vector candidates for the current block, and a motion vectorcandidate list is generated by using the emotion vector candidates. Themotion vector candidate of the current block can be derived by using thegenerated motion vector candidate list. The motion information of thecurrent block may be determined based on the derived motion vectorcandidate. The motion vectors of the collocated blocks or the motionvectors of the blocks adjacent to the collocated blocks may be referredto as temporal motion vector candidates, and the motion vectors of thereconstructed neighboring blocks may be referred to as spatial motionvector candidates.

The encoding apparatus 100 may calculate a motion vector difference(MVD) between the motion vector of the current block and the motionvector candidate and may perform entropy encoding on the motion vectordifference (MVD). In addition, the encoding apparatus 100 may performentropy encoding on a motion vector candidate index and generate abitstream. The motion vector candidate index may indicate an optimummotion vector candidate among the motion vector candidates included inthe motion vector candidate list. The decoding apparatus may performentropy decoding on the motion vector candidate index included in thebitstream and may select a motion vector candidate of a decoding targetblock from among the motion vector candidates included in the motionvector candidate list by using the entropy-decoded motion vectorcandidate index. In addition, the decoding apparatus 200 may add theentropy-decoded MVD and the motion vector candidate extracted throughthe entropy decoding, thereby deriving the motion vector of the decodingtarget block.

The bitstream may include a reference picture index indicating areference picture. The reference picture index may be entropy-encoded bythe encoding apparatus 100 and then signaled as a bitstream to thedecoding apparatus 200. The decoding apparatus 200 may generate aprediction block of the decoding target block based on the derivedmotion vector and the reference picture index information.

Another example of the method of deriving the motion information of thecurrent may be the merge mode. The merge mode may mean a method ofmerging motion of a plurality of blocks. The merge mode may mean a modeof deriving the motion information of the current block from the motioninformation of the neighboring blocks. When the merge mode is applied,the merge candidate list may be generated using the motion informationof the reconstructed neighboring blocks and/or the motion information ofthe collocated blocks. The motion information may include at least oneof a motion vector, a reference picture index, and an inter-pictureprediction indicator. The prediction indicator may indicateone-direction prediction (L0 prediction or L1 prediction) ortwo-direction predictions (L0 prediction and L1 prediction).

The merge candidate list may be a list of motion information stored. Themotion information included in the merge candidate list may be at leasteither one of the zero merge candidate and new motion information thatis a combination of the motion information (spatial merge candidate) ofone neighboring block adjacent to the current block, the motioninformation (temporal merge candidate) of the collocated block of thecurrent block, which is included within the reference picture, and themotion information exiting in the merge candidate list.

The encoding apparatus 100 may generate a bitstream by performingentropy encoding on at least one of a merge flag and a merge index andmay signal the bitstream to the decoding apparatus 200. The merge flagmay be information indicating whether or not to perform the merge modefor each block, and the merge index may be information indicating thatwhich neighboring block, among the neighboring blocks of the currentblock, is a merge target block. For example, the neighboring blocks ofthe current block may include a left neighboring block on the left sideof the current block, an upper neighboring block disposed above thecurrent block, and a temporal neighboring block temporally adjacent tothe current block.

The skip mode may be a mode in which the motion information of theneighboring block is applied to the current block as it is. When theskip mode is applied, the encoding apparatus 100 may perform entropyencoding on information of the fact that the motion information of whichblock is to be used as the motion information of the current block togenerate a bit stream, and may signal the bitstream to the decodingapparatus 200. The encoding apparatus 100 may not signal a syntaxelement regarding at least any one of the motion vector differenceinformation, the encoding block flag, and the transform coefficientlevel to the decoding apparatus 200.

The current picture reference mode may mean a prediction mode in which apreviously reconstructed region within a current picture to which thecurrent block belongs is used for prediction. Here, a vector may be usedto specify the previously-reconstructed region. Information indicatingwhether the current block is to be encoded in the current picturereference mode may be encoded by using the reference picture index ofthe current block. The flag or index indicating whether or not thecurrent block is a block encoded in the current picture reference modemay be signaled, and may be deduced based on the reference picture indexof the current block. In the case where the current block is encoded inthe current picture reference mode, the current picture may be added tothe reference picture list for the current block so as to be located ata fixed position or a random position in the reference picture list. Thefixed position may be, for example, a position indicated by a referencepicture index of 0, or the last position in the list. When the currentpicture is added to the reference picture list so as to be located atthe random position, the reference picture index indicating the randomposition may be signaled.

FIG. 6 is a view for explaining a process of transform and quantization.

As shown in FIG. 6, a quantized level may be generated by performingtransform and/or quantization process to a residual signal. The residualsignal may be generated as a difference between an original block and aprediction block (intra prediction block or inter prediction block).Here, the transform may include at least one among a primary transformand a secondary transform. A transform coefficient may be generated byperforming the primary transform to the residual signal. A secondarytransform coefficient may be generated by performing the secondarytransform to the transform coefficient.

The primary transform may be performed by using at least one among aplurality of predefined transform methods. For example, the plurality ofpredefined transform methods may comprise DCT (DCT (Discrete CosineTransform), DST (Discrete Sine Transform) or KLT (Karhunen-LoeveTransform) based transform, etc. The secondary transform may beperformed on a transform coefficient generated after performing theprimary transform. The transform method applied for the primarytransform and/or the secondary transform may be determined according toat least one among coding parameters of the current block and/or aneighbor block. Alternatively, transform information indicating atransform method may be signaled.

A quantized level may be generated by performing quantization on theresult of performing the primary transform and/or the secondarytransform or a residual signal. The quantized level may be scannedaccording to at least one among up-right diagonal scan, vertical scanand horizontal scan based on at least one among an intra predictionmode, a size/shape of a block. For example, coefficients of a block maybe changed into a one-dimensional vector form by scanning thecoefficients using up-right diagonal scan. A vertical scan which scanscoefficients of two-dimensional block form in a column direction or ahorizontal scan which scans coefficients of two-dimensional block formin a row direction may be used based on a transform block size and/orintra prediction mode instead of the up-right diagonal scan. The scannedquantization level may be included in a bitstream after being entropyencoded.

A decoder may generate a quantized level by entropy decoding abitstream. the quantized level may be inverse scanned and arranged intoa two dimensional block form. Here, at least one among up-right diagonalscan, vertical scan and horizontal scan may be performed as an inversescanning method.

The quantized level may be inverse quantized. A secondary inversetransform may be performed according to whether to perform the secondaryinverse transform. A reconstructed residual signal may be generated byperforming a primary inverse transform on the result of performing thesecondary inverse transform according to whether to perform the primaryinverse transform.

Hereinafter, a block partition method and apparatus according to thepresent invention will be described.

In order to partition a current block, partition information of thecurrent block may be derived. Partition information of a block may bederived by a method and apparatus including at least one of deriving ina coding tree unit level, deriving in a coding unit level, and derivingin a picture parameter set (PPS) level. Herein, the current block maymean a luma block or a chroma block. Any one of the luma block or thechroma block may be independently partitioned from the other one.Alternatively, any one of the two blocks may be partitioned bydependently referencing partition information of the other one. Forexample, when the current block is a chroma block, information of acorresponding luma block may be referenced. Alternatively, when thecurrent block is a luma block, information of a corresponding chromablock may be referenced. Hereinafter, the current block that becomes apartition target may be a chroma block.

In deriving in a CTU level, information indicating whether or not eachof quad-tree (QT) partitioning and binary-tree (BT) partitioning of achroma block is identical to a corresponding luma block may be used.Alternatively, the QT partitioning of the chroma block may be identicalto the corresponding luma block, and the BT partitioning of the chromablock may be selectively identical to or different from thecorresponding luma block. Information (for example, indicator such asflag, etc.) may be signaled for this. Alternatively, both the QTpartitioning and the BT partitioning of the chroma block may beidentical to or different from the corresponding luma block, andinformation indicating the above may be signaled.

In deriving in a CU level, according to a block size or form or both,information indicating whether or not each of QT partitioning and BTpartitioning of a chroma block is identical to a corresponding lumablock may be used. Alternatively, according to a block size or form orboth, information indicating that QT partitioning of the chroma block isidentical to the corresponding luma block, and indicating whether or notBT partitioning of the chroma block is selectively identical to ordifferent from the corresponding luma block may be used. Alternatively,according to a block size or form or both, information indicatingwhether or not both QT partitioning and BT partitioning of the chromablock are identical to the corresponding luma block may be used.

In deriving in a PPS level, information that may be used in the derivingin a CTU level and the deriving in a CU level may be signaled in a PPSlevel. Herein, a chroma block may be partitioned based on informationsignaled in a PPS level for a CU belonging to a specific picturereferencing the corresponding PPS.

Hereinafter, deriving in a coding tree unit (CTU) level will bedescribed with reference to FIG. 7 to FIG. 10.

A chroma block for a CU belonging to a CTU may be identicallypartitioned with a corresponding luma block, or may be partiallyidentically partitioned with a corresponding luma block. Alternatively,the chroma block may be independently partitioned with regardless of theluma block.

Information about a relation between partitioning of a chroma block andpartitioning of a corresponding luma block may be signaled in a CTUlevel. For example, at least one of an indicator indicating thatpartition information of a chroma block for a CU belonging to acorresponding CTU is derived from partition information of acorresponding luma block, an indicator indicating that the chroma blockis identically partitioned with the corresponding luma block, anindicator indicating that the chroma block is partially identicallypartitioned with the corresponding luma block, an indicator indicatingwhich partitioning (for example, QT partitioning or BT partitioning) forthe chroma block is identical to partitioning for the luma block, and anindicator indicating that the chroma block is partitioned withregardless of the corresponding luma block may be signaled in a CTUlevel.

The chroma block or the luma block may be at least one of a coding treeblock, a coding block, a prediction block, a transform block, and ablock having a predetermined size.

FIG. 7 is a view for illustrating deriving of block partitioninformation in a CTU level. In FIG. 7, each of (a), (b), and (c) maycorrespond to an example of signaling partition information of a chromablock in a CTU level.

In FIG. 7, ChromaSplitDerivedFlag may be information indicating whetheror not QT partition information of a chroma block may be derived from QTpartition information of a corresponding luma block. In the presentdescription, QT partition information of a block may be informationindicating whether or not a corresponding block may be partitioned in aquad-tree.

ChromaBTSplitModeDerivedFlag may be information indicating whether ornot BT partition information of a chroma block is derived from BTpartition information of a corresponding luma block. In the presentdescription, BT partition information of a block may be information ofat least one of whether or not a corresponding block is partitioned in abinary-tree, a direction (horizontal partitioning or verticalpartitioning) of BT partitioning, whether or not asymmetric partitioningis, and a ratio of asymmetric partitioning.

ChromaQTBTDerivedFlag may be information indicating whether or not atleast one of QT partition information and BT partition information of achroma block is derived from at least one of QT partition informationand BT partition information of a corresponding luma block.

QTSplitFlag may be QT partition information of a current CU in a CUlevel. ChromaQTSplitFlag may be QT partition information of a chromablock.

BTSplitMode may be BT partition information of a current CU in a CUlevel. ChromaBTSplitMode may be BT partition information of a chromablock.

QTBT may be a meaning indicating both QT and BT.

Describing an example (a) shown in FIG. 7, partition information of achroma block may be derived based on at least one of an indicatorindicating whether or not QT partition information of a correspondingluma block is used, and an indicator indicating whether or not BTpartition information of the corresponding luma block is used.

In detail, when the indicator indicating whether or not QT partitioninformation of the corresponding luma block is used (for example,ChromaSplitDerivedFlag) is 0, partition information of the chroma blockmay not be derived from partition information of the corresponding lumablock. Herein, partition information of the chroma block (for example,ChromaQTSplitFlag or ChromaBTSplitMode or both) may be signaled in a CUlevel. In other words, the encoder may signal partition information of achroma block for a CU belonging to a CTU in a CU level, and the decodermay partition the chroma block based on the signaled information.

For example, when ChromaSplitDerivedFlag is 1, an indicator indicatingwhether or not BT partition information of a corresponding luma block(for example, ChromaBTSplitModeDerivedFlag) may be additionallysignaled. When ChromaBTSplitModeDerivedFlag is 0, BT partitioninformation of a chroma block for a CU belonging to a CTU may not bederived from BT partition information of a corresponding luma block.Herein, BT partition information of the chroma block may be signaled ina CU level. In addition, QT partition information of the chroma blockmay be derived from QT partition information of the corresponding lumablock. In other words, the encoder may not signal QT partitioninformation of the chroma block for a CU belonging to a CTU in a CUlevel, and the decoder may identically partition the chroma block withQT partitioning of the corresponding luma block.

For example, when ChromaSplitDerivedFlag is 1 andChromaBTSplitModeDerivedFlag is 1, QT partition information and BTpartition information of a chroma block for a CU belonging to a CTU maybe derived from QT partition information and BT partition information ofa corresponding luma block. Herein, the encoder may not signal QTpartition information and BT partition information of the chroma blockfor a CU belonging to a CTU, and the decoder may identically partitionthe chroma block with QT and BT partitioning of the corresponding lumablock.

FIG. 8 is a view illustrating operations corresponding to the example(a) shown in FIG. 7. FIG. 8(a) shows operations of the encoder, and FIG.8(b) shows operations of the decoder.

In the encoder, as shown in FIG. 8(a), first, in step S801, a chromablock that is a partition target block may be specified. Then, in stepS802, a ChromaSplitDerivedFlag value for a current CTU may bedetermined. When ChromaSplitDerivedFlag is false, in order to determinean optimized QTBT partition form for the chroma block, in step S803,rate distortion optimization (RDO) may be performed. Then, in step S804,at least one of ChromaSplitDerivedFlag having a value being false, QTpartition information (Chroma SplitFlag) of the chroma block, and BTpartition information (Chroma BTSplitMode) of the chroma block may beencoded.

When ChromaSplitDerivedFlag is true in step S802, QT partitioninformation of the chroma block may be derived from QT partitioninformation of a corresponding luma block in step S805. Then, in orderto determine whether or not BT partition information of the chroma blockis derived from BT partition information of the corresponding lumablock, in step S806, a ChromaBTSplitModeDerivedFlag value may bedetermined. When ChromaBTSplitModeDerivedFlag is false, in order todetermine an optimized BT partition form for the chroma block, in stepS807, rate distortion optimization may be performed. After, in stepS808, ChromaSplitDerivedFlag having a value being true, andChromaBTSplitModeDerivedFlag having a value being false and the BTpartition information of the chroma block may be encoded

When ChromaBTSplitModeDerivedFlag is true in step S806, BT partitioninformation of the chroma block may be derived from BT partitioninformation of the corresponding luma block in step S809. Then, in stepS810, ChromaSplitDerivedFlag and ChromaBTSplitModeDerivedFlag which havevalues being true may be encoded

In the decoder, as shown in FIG. 8(b), first, in step S811, a chromablock that becomes a partition target block may be specified. Then, instep S812, a ChromaSplitDerivedFlag value that is signaled in a CTUlevel may be determined. When ChromaSplitDerivedFlag is false, in stepS813, QT partition information of the chroma block or BT partitioninformation of the chroma block or both may be decoded from a bitstream.

When ChromaSplitDerivedFlag is true, in step S814, QT partitioninformation of the chroma block may be derived from QT partitioninformation of the corresponding luma block. Then, in step S815, aChromaBTSplitModeDerivedFlag value may be determined. WhenChromaBTSplitModeDerivedFlag is false, in step S816, BT partitioninformation of the chroma block may be decoded from a bitstream. WhenChromaBTSplitModeDerivedFlag is true in step S815, BT partitioninformation of the chroma block may be derived from BT partitioninformation of the corresponding luma block in step S817. The decodermay partition the chroma block based on partition information derived ordecoded from at least one of steps S813, S814, S816, and S817.

Describing another example (b) of the present invention by referencingagain FIG. 7, it may be set that QT partition information of a chromablock is derived from QT partition information of a corresponding lumablock. The above setting may be performed by using information signaledin a CTU level or a level higher than the CTU. The higher level may beat least one level of a video, a sequence, a picture, a slice, and atile. Alternatively, without signaling additional information, it may beset as a default for the encoder and the decoder to derive QT partitioninformation of the chroma block from QT partition information of thecorresponding luma block.

When QT partition information of the chroma block is derived from QTpartition information of the corresponding luma block, QT partitioninformation of the chroma block for a CU belonging to a CTU may not besignaled. Herein, an indicator indicating whether or not BT partitioninformation of the corresponding luma block is used (for example,ChromaBTSplitModeDerivedFlag) may be signaled.

When ChromaBTSplitModeDerivedFlag is 0, BT partition information of thechroma block for the CU belonging to the CTU may not be derived from BTpartition information of the corresponding luma block. Herein, BTpartition information of the chroma block may be signaled in a CU level.

When ChromaBTSplitModeDerivedFlag is 1, BT partition information of thechroma block for the CU belonging to the CTU may be derived from BTpartition information of the corresponding luma block. Herein, theencoder may not signal QT partition information and BT partitioninformation of the chroma block for the CU belonging to the CTU, and thedecoder may identically partition the chroma block with QT partitioningand BT partitioning of the corresponding luma block.

FIG. 9 is a view illustrating operations corresponding to the example(b) shown in FIG. 7. FIG. 9(a) shows operations of the encoder, and FIG.9(b) shows operations of the decoder.

In the encoder, as shown in FIG. 9(a), first, in step S901, a chromablock that becomes a partition target block may be specified. In stepS902, QT partition information of the chroma block may be derived fromQT partition information of a corresponding luma block. Then, in orderto determine whether or not BT partition information of the chroma blockis derived from BT partition information of the corresponding lumablock, in step S903, a ChromaBTSplitModeDerivedFlag value may bedetermined. When ChromaBTSplitModeDerivedFlag is false, in order todetermine an optimized BT partition form for the chroma block, ratedistortion optimization may be performed in step S904. Then, in stepS905, ChromaBTSplitModeDerivedFlag having a value being false, and BTpartition information of the chroma block may be encoded.

When ChromaBTSplitModeDerivedFlag is true in step S903, BT partitioninformation of the chroma block may be derived from BT partitioninformation of the corresponding luma block in step S906. Then, in stepS907, ChromaBTSplitModeDerivedFlag having a value being true may beencoded.

In the decoder, as shown in FIG. 9(b), first, in step S911, a chromablock that becomes a partition target block may be specified. In stepS912, QT partition information of the chroma block may be derived fromQT partition information of the corresponding luma block. Then, in stepS913, a ChromaBTSplitModeDerivedFlag value may be determined. WhenChromaBTSplitModeDerivedFlag is false, in step S914, BT partitioninformation of the chroma block may be decoded from a bitstream. WhenChromaBTSplitModeDerivedFlag is true in step S913, BT partitioninformation of the chroma block may be derived from BT partitioninformation of the corresponding luma block in step S915. The decodermay partition the chroma block based on partition information derived ordecoded from at least one of step S912, step S914, and step S915.

Describing an example (c) of the present invention by referencing agingFIG. 7, according to an indicator indicating whether or not partitioninformation of a corresponding luma block is used, at least one of QTblock partition information and BT block partition information of achroma block may be derived from at least one of QT block partitioninformation and BT block partition information of a corresponding lumablock.

For example, when the indicator indicating whether or not the partitioninformation of the corresponding luma block (for example,ChromaQTBTDerivedFlag) is used is 0, at least one of QT partitioninformation and BT partition information of the chroma block for a CUbelonging to a CTU may not be derived from at least one of QT partitioninformation and BT partition information of the corresponding lumablock. Herein, QT partition information or BT partition information orboth of the chroma block which is not derived may be signaled in a CUlevel. In other words, the encoder may signal the QT partitioninformation or the BT partition information or both of the chroma blockfor the CU belonging to the CTU in a CU level, and the decoder maypartition the chroma block based on the signaled information.

For example, when ChromaQTBTDerivedFlag is 1, at least one of QTpartition information and BT partition information of the chroma blockfor the CU belonging to the CTU may be derived from at least one of QTpartition information and BT partition information of the correspondingluma block. Herein, the encoder may not signal QT partition informationor BT partition information or both of the chroma block for the CUbelonging to the CTU, and the decoder may identically partition thechroma block with QT partitioning or BT partitioning or both of thecorresponding luma block.

FIG. 10 is a view for illustrating operations corresponding to theexample (c) shown in FIG. 7. FIG. 10(a) shows operations of the encoder,and FIG. 10(b) shows operations of the decoder.

In the encoder, as shown in FIG. 10(a), first, in step S1001, a chromablock that becomes a partition target block may be specified. Then, inorder to determine whether or not QTBT partition information of thechroma block is derived from QTBT partition information of acorresponding luma block, in step S1002, a ChromaQTBTDerivedFlag valuemay be determined. When ChromaQTBTDerivedFlag is false, in order todetermine an optimized QTBT partition form for the chroma block, in stepS1003, rate distortion optimization may be performed. Then, in stepS1004, at least one of ChromaQTBTDerivedFlag having a value being false,QT partition information of the chroma block, and BT partitioninformation of the chroma block may be encoded.

When ChromaQTBTDerivedFlag is true in step S1002, QT partitioninformation and BT partition information of the chroma block may berespectively derived from QT partition information and BT partitioninformation of the corresponding luma block in steps S1005 and S1006.Then, in step S1007, ChromaQTBTDerivedFlag having a value being true maybe encoded.

In the decoder, as shown in FIG. 10(b), first, in step S1011, a chromablock that becomes a partition target block may be specified. Then, instep S1012, a ChromaQTBTDerivedFlag value may be determined. WhenChromaQTBTDerivedFlag is false, in step S1013, QT partition informationor BT partition information or both of the chroma block may be decodedfrom a bitstream. When ChromaQTBTDerivedFlag is true in step S1012, QTpartition information or BT partition information or both of the chromablock may be derived from QT partition information or BT partitioninformation or both of the corresponding luma block in steps S1014 andS1015. The decoder may partition the chroma block based on partitioninformation derived or decoded from at least one of step S1013, stepS1014, and step S1015.

Hereinafter, deriving in a coding unit (CU) level will be described withreference to FIG. 11 to FIG. 14.

Whether or not partition information of a chroma block is derived frompartition information of a corresponding luma block may be determinedbased on a block size of a CU belonging to a CTU. Herein, the block sizemay mean a size of a chroma block. In addition, as described above,partitioning of a chroma block and partitioning of a luma block may beidentical, may be partially identical, or may be independentlydetermined.

For example, a block size may be compared with an arbitrary thresholdvalue. The threshold value may be a value preset in the encoder/decoder.Alternatively, it may be signaled in at least one level of a video, asequence, a picture, a slice, a tile, and a CTU.

Information about a relation between partitioning of the chroma blockand partitioning of the corresponding luma block may be signaled in aCTU level. Information that may be signaled in a CTU level is the sameas the deriving in the CTU level described with reference to FIG. 7. Inaddition, the block may be at least one of a coding tree block, a codingblock, a prediction block, a transform block, and a block having apredetermined size.

FIG. 11 is a view for illustrating deriving of block partitioninformation in a CU level. In FIG. 11, each of (a), (b), and (c) maycorrespond to an example of signaling partition information of a blockin a CTU level for deriving block partition information.

Terms identically used in FIG. 7 and FIG. 11 among used terms may haveidentical meanings.

In the example described with reference to FIG. 11, partitioninformation of a chroma block may be derived based on at least one of ablock size of a CU, an indicator indicating whether or not QT partitioninformation of a corresponding luma block is used, and an indicatorindicating whether or not BT partition information of a correspondingluma block is used.

In addition, in the example described with reference to FIG. 11, when asize of a chroma block is smaller than a predetermined threshold value,partition information of the chroma block may not be derived frompartition information of a corresponding luma block, and may be signaledin a CU level. Herein, the encoder may signal QT partition informationor BT partition information or both of the chroma block for a CU inwhich the size of the chroma block is smaller than a threshold value ina CU level, and the decoder may partition the chroma block based oninformation signaled for the CU in which the size of the chroma block issmaller than the threshold value.

In FIG. 11, when a size of the chroma block is greater than apredetermined threshold value, partition information of the chroma blockmay be obtained according to the example described with reference toFIG. 7. In other words, among CUs belonging to a CTU, for a CU in whicha size of the chroma block is greater than a predetermined thresholdvalue, QT partition information or BT partition information or both ofthe chroma block may be signaled or derived according to the exampledescribed with reference to FIG. 7. Herein, the encoder may signal ormay not signal in CU level QT partition information or BT partitioninformation or both of the chroma block for a CU in which the size ofthe chroma block is greater than the threshold value among CUs belongingto a CTU, and the decoder may partition the chroma block based oninformation signaled for the CU in which the size of the chroma block isgreater than the threshold value among CUs belonging to the CTU, orbased on information derived from the corresponding luma block.

FIG. 12 is a view for illustrating operations corresponding to theexample (a) shown in FIG. 11. FIG. 12(a) shows operations of theencoder, and FIG. 12(b) shows operations of the decoder.

In the encoder, as shown in FIG. 12(a), first, in step S1201, a chromablock that becomes a partition target block may be specified. Then, instep S1202, a block size may be compared with a predetermined thresholdvalue. When the block size is not greater than the threshold value, inorder to determine an optimized QTBT partition form for the chromablock, in step S1203, rate distortion optimization may be performed.Then, in step S1204, at least one of ChromaSplitDerivedFlag having avalue being false, QT partition information of the chroma block, and BTpartition information of the chroma block may be encoded. When the blocksize is greater than the threshold value in step S1202, steps S1203 toS1211 may be performed, and the above steps may substantiallyrespectively correspond to steps S802 to 810 of FIG. 8(a). In otherwords, in FIG. 12(a), when the block size is greater than the thresholdvalue, operations of the encoder are the same as described in FIG. 8(a).Accordingly, descriptions of overlapped operations will be omitted.

In the decoder, as shown in FIG. 12(b), first, in step S1221, a chromablock that becomes a partition target block may be specified. Then, instep S1222, a block size may be compared with a predetermined thresholdvalue. When the block size is not greater than the threshold value, instep S1223, QT partition information or BT partition information or bothof the chroma block may be decoded from a bitstream.

When the block size is greater than the threshold value in step S1222,steps S1223 to S1228 may be performed, and the above steps maysubstantially respectively correspond to steps S812 to S817 of FIG.8(b). In other words, in FIG. 12(b), when the block size is greater thanthe threshold value, operations of the decoder are the same as describedin FIG. 8(b). Accordingly, descriptions of overlapped operations will beomitted.

FIG. 13 is a view for illustrating operations corresponding to theexample (b) shown in FIG. 11. FIG. 13(a) shows operation of the encoder,and FIG. 13(b) shows operations of the decoder.

In the encoder, as shown in FIG. 13(a), first, in step S1301, a chromablock that becomes a partition target block may be specified. Then, instep S1302, a block size may be compared with a predetermined thresholdvalue. When the block size is not greater than the threshold value, inorder to determine an optimized QTBT partition form for the chromablock, in step S1303, rate distortion optimization may be performed.Then, in step S1304, QT partition information or BT partitioninformation or both of the chroma block may be encoded.

When the block size is greater than the threshold value in step S1302,steps S1305 to S1310 may be performed, and the above steps may besubstantially respectively correspond to steps S902 to S907 of FIG.9(a). In other words, in FIG. 13(a), when the block size is greater thanthe threshold value, operations of the encoder are the same as describedin FIG. 9(a). Accordingly, descriptions of overlapped operations will beomitted.

In the decoder, as shown in FIG. 13(b), first, in step S1311, a chromablock that becomes a partition target block may be specified. Then, instep S1312, a block size may be compared with a predetermined thresholdvalue. When the block size is not greater than the threshold value, instep S1313, QT partition information or BT partition information or bothof the chroma block may be decoded from a bitstream.

When the block size is greater than the threshold value in step S1312,steps S1314 to S1317 may be performed, and the above steps maysubstantially respectively correspond to steps S912 to S915 of FIG.9(b). In other words, in FIG. 13(b), when the block size is greater thanthe threshold value, operations of the decoder are the same as describedin FIG. 9(b). Accordingly, descriptions of overlapped operations will beomitted.

FIG. 14 is a view for illustrating operations corresponding to theexample (c) shown in FIG. 11. FIG. 14(a) shows operations of theencoder, and FIG. 14(b) shows operations of the decoder.

In the encoder, as shown in FIG. 14(a), first, in step S1401, a chromablock that becomes a partition target block may be specified. Then, instep S1402, a block size may be compared with a predetermined thresholdvalue. When the block size is not greater than the threshold value, inorder to determine an optimized QTBT partition form for the chromablock, in step S1403, rate distortion optimization may be performed.Then, in step S1404, QT partition information or BT partitioninformation or both of the chroma block may be encoded.

When the block size is greater than the threshold value in step S1402,steps S1403 to S1408 may be performed, and the above steps maysubstantially respectively correspond to steps S1002 to S1007 of FIG.10(a). In other words, in FIG. 14(a), when the block size is greaterthan the threshold value, operations of the encoder are the same asdescribed in FIG. 10(a). Accordingly, descriptions of overlappedoperations will be omitted.

In the decoder, as shown in FIG. 14(b), first, in step S1411, a chromablock that becomes a partition target block may be specified. Then, instep S1412, a block size may be compared with a predetermined thresholdvalue. When the block size is not greater than the threshold value, instep S1413, QT partition information or BT partition information or bothof the chroma block may be decoded from a bitstream.

When the block size is greater than the threshold value in step S1412,steps S1413 to S1416 may be performed, and the above steps maysubstantially respectively correspond to steps S1012 to S1015 of FIG.10(b). In other words, in FIG. 14(b), when the block size is greaterthan the threshold value, operations of the decoder are the same asdescribed in FIG. 10(b). Accordingly, descriptions of overlappedoperations will be omitted.

Hereinafter, deriving in a PPS level will be described with reference toFIG. 15.

Partition information of a chroma block for a CU belonging to a specificpicture may be derived from partition information of a correspondingluma block. Partitioning of the chroma block for the CU belonging to thespecific picture may be identically or partially identically performedwith partitioning of the corresponding luma block. Alternatively, thechroma block may be independently partitioned with regardless of theluma block.

Partition information of a block may be derived based on a block size.Herein, the block may mean a chroma block. For example, a size of thechroma block may be compared with an arbitrary threshold value.Descriptions of the arbitrary threshold value are the same as describedwith reference to FIG. 11.

Information about a relation between partitioning of a chroma block andpartitioning of a corresponding luma block may be signaled in a PPSlevel. For example, at least one of an indicator indicating whether ornot partition information of the chroma block for a CU belonging to aspecific picture is derived from partition information of thecorresponding luma block, an indicator indicating that the chroma blockis identically partitioned with the corresponding luma block, anindicator indicating that the chroma block is partially identicallypartitioned with the corresponding luma block, an indicator representingwhich partitioning (for example, QT partition or BT partition) amongpartitionings for the chroma block is identical with partitioning forthe luma block, and an indicator indicating that the chroma block ispartitioned with regardless of the corresponding luma block may besignaled in a PPS level.

FIG. 15 is a view for illustrating deriving of block partitioninformation in a PPS level. In FIG. 15, each of (a), (b), (c), (d), (e),and (f) may correspond to an example of signaling partition informationof a chroma block in a PPS level.

Terms identically used in FIG. 7, FIG. 11, and FIG. 15 among used termsmay have identical meanings.

In FIG. 15, ChromaSplitDerivedEnableFlag may be information indicatingwhether or not QT partition information of a chroma block is derivedfrom QT partition information of a corresponding luma block.ChromaBTSplitModeDerivedEnableFlag may be information indicating whetheror not BT partition information of the chroma block is derived from BTpartition information of the corresponding luma block.ChromaQTBTDerivedEnableFlag may be information indicating whether or notat least one of QT partition information and BT partition information ofthe chroma block is derived from at least one of QT partitioninformation and BT partition information of the corresponding lumablock.

Information used in FIG. 15 such as ChromaSplitDerivedEnableFlag,ChromaBTSplitModeDerivedEnableFlag, ChromaQTBTDerivedEnableFlag, etc. isinformation signaled in a PPS level. When the above flag is 0, it may bedetermined that partition information of the chroma block for all CUsbelonging to a specific picture referencing the corresponding PPS isadditionally signaled rather than being derived from partitioninformation of the corresponding luma block. Herein, partitioninformation of the chroma block may be signaled in a CU level.

When the above flag is 1, partition information of the chroma block forthe CU belonging to the specific picture referencing the correspondingPPS may be derived from partition information of the corresponding lumablock. Herein, partition information of the chroma block may not besignaled in a CU level.

For example, each of (a), (b), and (c) of FIG. 15 may correspond to (a),(b), and (c) of FIG. 7. Herein, ChromaSplitDerivedEnableFlag,ChromaBTSplitModeDerivedEnableFlag, and ChromaQTBTDerivedEnableFlag ofFIG. 15 may respectively correspond to ChromaSplitDerivedFlag,ChromaBTSplitModeDerivedFlag, and ChromaQTBTDerivedFlag of FIG. 7.However, there is a difference in that in FIG. 15, an indicator issignaled in a PPS level, and in FIG. 7, an indicator is signaled in aCTU level. Accordingly, there is a difference in that information issignaled in different levels, thus obtaining partition information of achroma block according to each indicator value in (a), (b), and (c) ofFIG. 15 may be identically performed with obtaining of partitioninformation of a chroma block described with reference to (a), (b), and(c) of FIG. 7.

FIG. 16 is a view for illustrating operations corresponding to theexample (a) shown in FIG. 15. FIG. 16(a) shows operations of theencoder, and FIG. 16(b) shows operations of the decoder.

Comparing FIG. 16 with FIG. 8, ChromaSplitDerivedFlag andChromaBTSplitModeDerivedFlag of FIG. 8 are respectively changed toChromaSplitDerivedEnableFlag and ChromaBTSplitModeDerivedEnableFlag inFIG. 16, the encoder and the decoder substantially perform identicaloperations. Accordingly, descriptions of respective steps of FIG. 16 arethe same as corresponding steps of FIG. 8, thus descriptions ofoverlapped operations will be omitted.

FIG. 17 is a view for illustrating operations corresponding to theexample (b) shown in FIG. 15. FIG. 17(a) shows operations of theencoder, and FIG. 17(b) shows operations of the decoder.

Comparing FIG. 17 with FIG. 9, ChromaBTSplitModeDerivedFlag of FIG. 9 ischanged to ChromaBTSplitModeDerivedEnableFlag in FIG. 17, and theencoder and the decoder substantially perform identical operations.Accordingly, descriptions of respective steps of FIG. 17 are the same ascorresponding steps of FIG. 9, thus descriptions of overlappedoperations will be omitted.

FIG. 18 is a view for illustrating operations corresponding to theexample (c) shown in FIG. 15. FIG. 18(a) shows operations of theencoder, and FIG. 18(b) shows operations of the decoder.

Comparing FIG. 18 with FIG. 10, ChromaQTBTDerivedFlagof FIG. 10 ischanged to ChromaQTBTDerivedEnableFlag in FIG. 18, and the encoder andthe decoder substantially perform identical operations. Accordingly,descriptions of respective steps of FIG. 18 are the same ascorresponding steps of FIG. 10, thus descriptions of overlappedoperations will be omitted.

Similarly, each of (d), (e), and (f) of FIG. 15 may correspond to (a),(b), and (c) of FIG. 11. Herein, ChromaSplitDerivedEnableFlag,ChromaBTSplitModeDerivedEnableFlag, and ChromaQTBTDerivedEnableFlag ofFIG. 15 may respectively correspond to ChromaSplitDerivedFlag,ChromaBTSplitModeDerivedFlag, and ChromaQTBTDerivedFlag in FIG. 11.However, there is a difference in that an indicator is signaled in a PPSlevel in FIG. 15, and an indicator is signaled in a CTU level in FIG.11.

Accordingly, obtaining of partition information of a chroma blockaccording to a respective indicator value in (d), (e), and (f) of FIG.15 may be identically performed with obtaining of partition informationof a chroma block which is described with reference to (a), (b), and (c)of FIG. 11.

FIG. 19 is a view for illustrating operations corresponding to theexample (d) shown in FIG. 15. FIG. 19(a) shows operations of theencoder, and FIG. 19(b) shows operations of the decoder.

Comparing FIG. 19 with FIG. 12, ChromaSplitDerivedFlag andChromaBTSplitModeDerivedFlag of FIG. 12 are respectively changed toChromaSplitDerivedEnableFlag and ChromaBTSplitModeDerivedEnableFlag inFIG. 19, and the encoder and the decoder substantially perform identicaloperations. Accordingly, descriptions of respective steps of FIG. 19 arethe same as corresponding steps of FIG. 12, thus descriptions ofoverlapped operations will be omitted.

FIG. 20 is a view for illustrating operations corresponding to theexample (e) shown in FIG. 15. FIG. 20(a) shows operations of theencoder, and FIG. 20(b) shows operations of the decoder.

Comparing FIG. 20 with FIG. 13, ChromaBTSplitModeDerivedFlag of FIG. 13is changed to ChromaBTSplitModeDerivedEnableFlag in FIG. 20, and theencoder and the decoder substantially perform identical operations.Accordingly, descriptions of respective steps of FIG. 20 are the same ascorresponding steps of FIG. 13, thus descriptions of overlappedoperations will be omitted.

FIG. 21 is a view for illustrating operations corresponding to theexample (f) shown FIG. 15. FIG. 21(a) shows operations of the encoder,and FIG. 21(b) shows operations of the decoder.

Comparing FIG. 21 with FIG. 14, ChromaQTBTDerivedFlag of FIG. 14 ischanged to ChromaQTBTDerivedEnableFlag in FIG. 21, and the encoder andthe decoder substantially perform identical operations. Accordingly,descriptions of respective steps of FIG. 21 are the same ascorresponding steps of FIG. 14, thus descriptions of overlappedoperations will be omitted.

Different from the example described with reference to FIG. 15, when aflag signaled in a PPS level such as ChromaSplitDerivedEnableFlag,ChromaBTSplitModeDerivedEnableFlag, ChromaQTBTDerivedEnableFlag, etc. is1, an indicator indicating whether or not partition information of achroma block in a level lower than the PSS (for example, slice level,tile level alternatively CTU level, etc.) is derived from partitioninformation of a corresponding luma block may be re-signaled. When theindicator is re-signaled in a lower level, partition information of achroma block for a CU belonging to the corresponding lower level may beobtained based on the re-signaled indicator. Herein, for example, whenthe lower level is a CTU level, the example described with reference toFIG. 7 or FIG. 11 may be applied.

The example in which the indicator indicating the method of obtainingpartition information of the chroma block is signaled in a CTU orpicture level has been described with reference to FIG. 7 to FIG. 21.However, the present invention is not limited thereto. For example, anindicator indicating a method of obtaining partition information of achroma block may be signaled in at least one level of a video, asequence, a picture, a slice, a tile, a CTU, and a CU. In the respectivelevels, the indicator may be signaled by being included in a videoparameter set (VPS), a sequence parameter set (SPS), a picture parameterset (PPS), a slice header, a tile header, a CTU syntax structure, and aCU syntax structure.

In addition, as shown in FIG. 15(a), when at least two indicators (forexample, ChromaSplitDerivedEnableFlag andChromaBTSplitModeDerivedEnableFlag) are signaled, the indicators may berespectively signaled in different levels. For example,ChromaSplitDerivedEnableFlag may be signaled in a picture level, andChromaBTSplitModeDerivedEnableFlag may be signaled in a CTU level.Herein, when ChromaSplitDerivedEnableFlag is 1, QT partition informationof a chroma block for all CUs belonging to a corresponding picture maybe derived from QT partition information of a corresponding luma block.In addition, according to whether ChromaBTSplitModeDerivedEnableFlagthat is signaled in a CTU level is 0 or 1, BT partition information of achroma block may be signaled, or may be derived from BT partitioninformation of a corresponding luma block.

In the example described with reference to FIG. 7 to FIG. 21, a blockpartition method includes QT partitioning or BT partitioning or both.However, it is not limited thereto. The block partition method mayinclude partition methods of all forms that may be used for partitioningthe block such as asymmetric tree (AT) partitioning, triple tree (TT)partitioning, N-ary tree (NT) partitioning, etc.

In addition, a block partition type may include a specific partitiontype such as horizontal partitioning, vertical partitioning, m:npartitioning, etc. by including the above block partition methods. Forexample, BT partitioning of horizontal partitioning and BT partitioningof vertical partitioning may be different types. Alternatively,respective AT partitioning having different asymmetric ratios (m:n) maybe different types. The above partition method may be applied incombination thereof. For example, when TT partitioning and ATpartitioning are applied in combination, TT partitioning differing fromat least one of a partition direction (horizontal or vertical), and anasymmetric ratio (l:m:n) may be different types from each other.

The present invention relates to whether to derive block partitioninformation of a first block from block partition information of acorresponding second block or to obtain block partition information ofthe first block from additionally signaled information. The blockpartition information may be information indicating at least one of theabove block partition methods, and the block partition type. Inaddition, the block partition information may be signaled in at leastone level of a VPS, a SPS, a PPS, a slice header, a tile header, a CTU,a CU, a prediction block, and a transform block.

FIG. 22 is a view showing various types of block partitioning.

FIG. 22(a) shows an example of QT partitioning. A current block may bepartitioned into four sub-blocks having identical sizes by QTpartitioning.

FIG. 22(b) shows an example of BT partitioning. A current block may bepartitioned into two sub-blocks having identical sizes by BTpartitioning.

FIG. 22(c) shows an example of applying AT partitioning to BTpartitioning. A current block may be partitioned into two sub-blockshaving sizes different from each other.

FIG. 22(d) shows an example of TT partitioning. A current block may bepartitioned into three sub-blocks by TT partitioning. When ATpartitioning is applied to TT partitioning, all or a part of the threesub-blocks may have identical sizes or have sizes different from eachother. When TT partitioning is uniform partitioning, three sub-blocksmay have identical sizes.

Partition information of a current block may be at least one ofindicators indicating whether or not a luma block is partitioned, apartition type of the luma block, whether or not a chroma block ispartitioned, a partition type of the chroma block, and whether or notpartition information of a corresponding luma block is used. Anindicator indicating whether or not partition information of acorresponding luma block is used may be an indicator representingwhether or not at least one of whether or not the corresponding lumablock is partitioned, and a partition type is used for the chroma block.The indicator indicating whether or not partition information of thecorresponding luma block is used may be present with regardless of anindicator representing partitioning and an indicator for a partitiontype. The partition information may be encoded/decoded in at least onelevel of a VPS, a SPS, a PPS, a slice header, a tile header, a CTU, aCU, a prediction block, and a transform block as described above.

Partition information of a first block (for example, chroma block) maybe determined by the above indicators. Then, based on the determinedpartition information, a chroma block may be partitioned. When partitioninformation of a second block (for example, corresponding luma block) isused, partition information of the chroma block may be determined basedon partition information of the corresponding luma block. When partitioninformation of the corresponding luma block is not used, partitioninformation of the chroma block may be additionally signaled. Whether ornot to use partition information of the corresponding luma block may bedetermined by using the above indicator. Alternatively, for a specificpartition method, it may be defined for the encoder/decoder to determinepartition information of a chroma block by using partition informationof a corresponding luma block without an additional determination. Forexample, the specific partition method may be at least one of QTpartitioning, BT partitioning, and QTBT partitioning. Determiningpartition information of a chroma block may be independently performedfor all or a part of all applicable partition methods. For example, whenall applicable partition methods are QT partitioning and BTpartitioning, determining partition information for QT partitioning maybe performed independent to determining partition information for BTpartitioning. Alternatively, partition information of a chroma block maybe identically determined for all applicable partition methods. Forexample, when it is determined to use partition information of acorresponding luma block, for all of QT partitioning and BTpartitioning, partition information of a chroma block may be determinedby using partition information of the corresponding luma block.

When both whether or not to partition and a partition type (partitiondirection or partition ratio) have to be specified, a part thereof maybe determined from partition information of a corresponding luma block.For example, whether or not to perform BT partitioning for a chromablock may be determined based on partition information of thecorresponding luma block, and whether BT partitioning is horizontalpartitioning or vertical partitioning may be determined based onadditionally signaled information. Herein, whether or not to usepartition information of the corresponding luma block may be signaled bythe above indicator, or may be pre-defined in the encoder/decoder.Alternatively, whether or not to partition the chroma block may bedetermined based on additionally signaled information, and a partitiontype may be determined from partition information of the correspondingluma block. For example, when the partitioning of the chroma block isdetermined based on additionally signaled information, the partitiontype may be determined from partition information of the correspondingluma block.

Partition information of a block (luma block or chroma block) may bedetermined based on at least one of a coding parameter, pictureinformation, slice information, tile information, coding modeinformation, a quantization parameter QP, a coding block flag CBF, ablock size, a block depth, a block form, entropy encoding method,partition information of a neighbor block, and a temporal layer level.The block may be at least one of a coding tree block, a coding block, aprediction block, a transform block, and a block having a predeterminedsize.

A chroma block may be partitioned by using QT partition information ofthe chroma block or BT partition information of the chroma block or both(first partition method). Alternatively, the chroma block may bepartitioned by using QT partition information of a corresponding lumablock and BT partition information of the chroma block (second partitionmethod). Alternatively, the chroma block may be partitioned by using QTpartition information of the corresponding luma block, and BT partitioninformation of the corresponding luma block (third partition method).Alternatively, the chroma block may be partitioned by using QT partitioninformation of the corresponding luma block, BT partition information ofthe corresponding luma block, and BT partition information of the chromablock (fourth partition method).

Which partition method among the first to fourth partition method to beapplied to a current block that becomes a partition target may bedetermined based on picture information. For example, informationrepresenting that the current picture is a specific picture by using aPPS may be encoded/decoded. When the current picture is the specificpicture, a specific partition method may be applied for a chroma blockincluded in the current picture. Which partition method will be appliedfor a block included in the specific picture may be signaled in a PPSlevel or a level higher than the PPS (VPS level, SPS level), or may bepre-defined in the encoder/decoder. Alternatively, a chroma blockincluded in the current picture may be partitioned based on informationof a previous picture. For example, when a chroma block included in theprevious picture is partitioned by using a second partition method, thechroma block included in the current picture may be partitioned by usingthe second partition method.

Which partition method among the first to the fourth partition methodswill be applied to a current block that becomes a partition target maybe determined based on slice information. For example, for a chromablock included in a specific slice, a specific partition method may beapplied. The specific slice may be at least one of an I slice, a Pslice, and a B slice. Which partition method will be applied to a blockincluded in the specific slice may be signaled in a slice level or alevel higher than the slice (VPS level, SPS level, PPS level), or may bepre-defined in the encoder/decoder. Alternatively, a partition method ofa chroma block included in the current slice may be determined based onpartition information of another slice. For example, the another slicemay be a neighbor slice or a previous slice.

Which partition method among the first to the fourth partition methodwill be applied to a current block that becomes a partition target maybe determined based on partition information of at least one neighborblock. The neighbor block may be at least one of a block positionedadjacent to a chroma block, and a block positioned adjacent to acorresponding luma block. For example, when the neighbor block ispartitioned by a first partition method, a chroma block may bepartitioned by the first partition method. Alternatively, the chromablock may be partitioned by using a part of partition information of theneighbor block. For example, the chroma block may be partitioned byusing one of the QT partition information and BT partition informationof the neighbor block.

Which partition method among the first to the fourth partition methodswill be applied to a current block that becomes a partition target maybe determined based on coding mode information. The coding modeinformation may be information representing whether the current block isan inter-predicted block or an intra-predicted block. Which partitionmethod will be applied to a block encoded in a specific coding mode maybe signaled in a prediction block level or a level higher than theprediction block (VPS level, SPS level, PPS level, slice level, tilelevel, CTU level, CU level), or may be pre-defined in theencoder/decoder.

Which partition method among the first to the fourth partition methodswill be applied to a current block that becomes a partition target maybe determined based on an intra coding mode. For example, when an intraprediction mode of the current block corresponds to a predeterminedrange, one of the first to the fourth partition methods may be used.Which partition method will be applied to a block encoded in an intraencoding mode of a specific range may be signaled in a block level (forexample, prediction block) or a level higher than the block (VPS level,SPS level, PPS level, slice level, tile level, CTU level, CU level), ormay be pre-defined in the encoder/decoder.

Which partition method among the first to the fourth partition methodswill be applied to a current block that becomes a partition target maybe determined based on a quantization parameter. The quantizationparameter may be a quantization parameter of a corresponding luma blockor a quantization parameter of a chroma block. For example, when aquantization parameter of the current block belongs to a predeterminedrange, one of the first to the fourth partition methods may be used.Which partition method will be applied to a block encoded in aquantization parameter of a specific range may be signaled in a blocklevel (for example, transform block) or a level higher than the block(VPS level, SPS level, PPS level, slice level, tile level, CTU level, CUlevel), or may be pre-defined in the encoder/decoder.

Which partition method among the first to the fourth partition methodswill be applied to a current block that becomes a partition target maybe determined based on a coding block flag CBF. The coding block flagmay be a coding block flag of a corresponding luma block or aquantization parameter of a chroma block. For example, when a codingblock flag of the current block has a predetermined value, one of thefirst to the fourth partition methods may be used. Which partitionmethod will be applied to a block having a specific value as a codingblock flag may be signaled in a block level (for example, coding block)or a level higher than the block (VPS level, SPS level, PPS level, slicelevel, tile level, CTU level, CU level), or may be pre-defined in theencoder/decoder.

Which partition method among the first to the fourth partition methodswill be applied to a current block that becomes a partition target maybe determined based on a block size. The block size may be a size of acorresponding luma block or a size of a chroma block. For example, whenthe current block has a predetermined size, one of the first to thefourth partition methods may be used. Which partition method will beapplied to a block having a specific size may be signaled in a blocklevel or a level higher than the block (VPS level, SPS level, PPS level,slice level, tile level, CTU level, CU level), or may be pre-defined inthe encoder/decoder.

Which partition method among the first to the fourth partition methodswill be applied to a current block that becomes a partition target maybe determined based on a partition depth of a block. The partition depthof the block may be a partition depth of a corresponding luma block or apartition depth of a chroma block. For example, when a partition depthof the current block has a predetermined depth, one of the first to thefourth partition methods may be used. Which partition method will beapplied to a block of a specific partition depth may be signaled in ablock level or a level higher than the block (VPS level, SPS level, PPSlevel, slice level, tile level, CTU level, CU level), or may bepre-defined in the encoder/decoder.

Which partition method among the first to the fourth partition methodsis applied to a current block that becomes partition target may bedetermined based on a block form. The block form may be a form of acorresponding luma block or a form of a chroma block. The block form maybe determined by an aspect ratio. For example, when a form of thecurrent block has a predetermined form, one of the first to the fourthpartition methods may be used. Which partition method will be applied toa block having a specific form may be signaled in a block level or alevel higher than the block (VPS level, SPS level, PPS level, slicelevel, tile level, CTU level, CU level), or may be pre-defined in theencoder/decoder.

Which partition method among the first to the fourth partition methodswill be applied to a current block that becomes a partition target maybe determined based on an entropy encoding method that is applied to ablock. The entropy encoding method may include various entropy encodingmethods by including context adaptive binary arithmetic coding (CABAC),and context adaptive variable length coding (CAVLC). For example, when aspecific entropy encoding method is applied to the current block, one ofthe first to the fourth partition methods may be used. Which partitionmethod will be applied to a block encoded by a specific entropy encodingmethod may be signaled in a block level or a level higher than the block(VPS level, SPS level, PPS level, slice level, tile level, CTU level, CUlevel), or may be pre-defined in the encoder/decoder.

Which partition method among the first to the fourth partition methodswill be applied to a current block that becomes a partition target maybe determined based on a temporal layer level of the current block. Thetemporal layer level may mean a temporal layer ID (temporal identifier)of a temporal layer to which the current block belongs. For example,when the current block belongs to a specific temporal layer level, oneof the first to the fourth partition methods may be used. Whichpartition method will be applied to a block belonging to a specifictemporal layer level may be signaled in a block level or a level higherthan the block (VPS level, SPS level, PPS level, slice level, tilelevel, CTU level, CU level), or may be pre-defined in theencoder/decoder.

Alternatively, according to a temporal layer level of a current block, apartition depth may be adaptively set. For example, according to whethera temporal layer ID of the current block corresponds to a specific valueor belongs to a specific value range, a partition depth for at least oneof QT partitioning and BT partitioning may be differently set. Herein, apartition depth of a block having a temporal layer level included in thespecific value or the specific value range may be signaled in a blocklevel or a level higher than the block (VPS level, SPS level, PPS level,slice level, tile level, CTU level, CU level), or may be pre-defined inthe encoder/decoder.

As described above, which partition method among the first to the fourthpartition methods will be applied to a current block that is a partitiontarget may be determined based on various types of coding information.However, it is not limited to the above examples. For example, inaddition to the coding information described above, a partition methodfor a current block may be determined based on other information. Inaddition, in order to partition the current block, in addition to thefirst to the fourth partition methods, various partition methodsaccording to a partition tree or partition form or both may be used.

The above embodiments may be performed in the same method in an encoderand a decoder.

A sequence of applying to above embodiment may be different between anencoder and a decoder, or the sequence applying to above embodiment maybe the same in the encoder and the decoder.

The above embodiment may be performed on each luma signal and chromasignal, or the above embodiment may be identically performed on luma andchroma signals.

A block form to which the above embodiments of the present invention areapplied may have a square form or a non-square form.

The above embodiment of the present invention may be applied dependingon a size of at least one of a coding block, a prediction block, atransform block, a block, a current block, a coding unit, a predictionunit, a transform unit, a unit, and a current unit. Herein, the size maybe defined as a minimum size or maximum size or both so that the aboveembodiments are applied, or may be defined as a fixed size to which theabove embodiment is applied. In addition, in the above embodiments, afirst embodiment may be applied to a first size, and a second embodimentmay be applied to a second size. In other words, the above embodimentsmay be applied in combination depending on a size. In addition, theabove embodiments may be applied when a size is equal to or greater thata minimum size and equal to or smaller than a maximum size. In otherwords, the above embodiments may be applied when a block size isincluded within a certain range.

For example, the above embodiments may be applied when a size of currentblock is 8×8 or greater. For example, the above embodiments may beapplied when a size of current block is 4×4 or greater. For example, theabove embodiments may be applied when a size of current block is 16×16or greater. For example, the above embodiments may be applied when asize of current block is equal to or greater than 16×16 and equal to orsmaller than 64×64.

The above embodiments of the present invention may be applied dependingon a temporal layer. In order to identify a temporal layer to which theabove embodiments may be applied may be signaled, and the aboveembodiments may be applied to a specified temporal layer identified bythe corresponding identifier. Herein, the identifier may be defined asthe lowest layer or the highest layer or both to which the aboveembodiment may be applied, or may be defined to indicate a specificlayer to which the embodiment is applied. In addition, a fixed temporallayer to which the embodiment is applied may be defined.

For example, the above embodiments may be applied when a temporal layerof a current image is the lowest layer. For example, the aboveembodiments may be applied when a temporal layer identifier of a currentimage is 1. For example, the above embodiments may be applied when atemporal layer of a current image is the highest layer.

A slice type to which the above embodiments of the present invention areapplied may be defined, and the above embodiments may be applieddepending on the corresponding slice type.

In the above-described embodiments, the methods are described based onthe flowcharts with a series of steps or units, but the presentinvention is not limited to the order of the steps, and rather, somesteps may be performed simultaneously or in different order with othersteps. In addition, it should be appreciated by one of ordinary skill inthe art that the steps in the flowcharts do not exclude each other andthat other steps may be added to the flowcharts or some of the steps maybe deleted from the flowcharts without influencing the scope of thepresent invention.

The embodiments include various aspects of examples. All possiblecombinations for various aspects may not be described, but those skilledin the art will be able to recognize different combinations.Accordingly, the present invention may include all replacements,modifications, and changes within the scope of the claims.

The embodiments of the present invention may be implemented in a form ofprogram instructions, which are executable by various computercomponents, and recorded in a computer-readable recording medium. Thecomputer-readable recording medium may include stand-alone or acombination of program instructions, data files, data structures, etc.The program instructions recorded in the computer-readable recordingmedium may be specially designed and constructed for the presentinvention, or well-known to a person of ordinary skilled in computersoftware technology field. Examples of the computer-readable recordingmedium include magnetic recording media such as hard disks, floppydisks, and magnetic tapes; optical data storage media such as CD-ROMs orDVD-ROMs; magneto-optimum media such as floptical disks; and hardwaredevices, such as read-only memory (ROM), random-access memory (RAM),flash memory, etc., which are particularly structured to store andimplement the program instruction. Examples of the program instructionsinclude not only a mechanical language code formatted by a compiler butalso a high level language code that may be implemented by a computerusing an interpreter. The hardware devices may be configured to beoperated by one or more software modules or vice versa to conduct theprocesses according to the present invention.

Although the present invention has been described in terms of specificitems such as detailed elements as well as the limited embodiments andthe drawings, they are only provided to help more general understandingof the invention, and the present invention is not limited to the aboveembodiments. It will be appreciated by those skilled in the art to whichthe present invention pertains that various modifications and changesmay be made from the above description.

Therefore, the spirit of the present invention shall not be limited tothe above-described embodiments, and the entire scope of the appendedclaims and their equivalents will fall within the scope and spirit ofthe invention.

INDUSTRIAL APPLICABILITY

The present invention may be used in encoding/decoding an image.

1. An image decoding method performed by an image decoding apparatus,the method comprising: determining a partitioning method of a currentblock as one of a first partitioning method and a second partitioningmethod based on slice information of a slice to which the current blockbelongs and information on partitioning of the current block; obtaininga coding block by partitioning the current block using the partitioningmethod; obtaining the prediction block of the coding block; andreconstructing the obtained coding block based on the prediction blockof the coding block, and wherein, when the partitioning method of thecurrent block is determined to the first partitioning method, a lumablock and a chroma block corresponding to the current block arepartitioned by a same partitioning structure, wherein, when thepartitioning method of the current block is determined to the secondpartitioning method, and a size of the current block is larger than apredetermined threshold value, the luma block and the chroma blockcorresponding to the current block are partitioned by a samepartitioning structure, and wherein, when the partitioning method of thecurrent block is determined to the second partitioning method, and thesize of the current block is less than or equal to the predeterminedthreshold value, the luma block and the chroma block corresponding tothe current block are partitioned by a different partitioning structurefrom each other.
 2. The image decoding method of claim 1, wherein theslice information is a slice type of the slice to which the currentblock belongs.
 3. The image decoding method of claim 2, wherein thedetermining the partitioning method of the current block comprisesdetermining whether a slice type of the slice to which the current blockbelongs is I slice or not.
 4. The image decoding method of claim 1,wherein the information on partitioning of the current block is signaledin a sequence parameter set (SPS).
 5. The image decoding method of claim1, wherein the information on partitioning of the current block is aflag information.
 6. The image decoding method of claim 1, wherein thepredetermined threshold value is
 64. 7. The image decoding method ofclaim 1, wherein, when the luma block and the chroma block correspondingto the current block is partitioned by the different method, whether thechroma block is partitioned or not is derived based on at least a sizeof a luma block corresponding to the chroma block and information onpartitioning of the luma block corresponding to the chroma block.
 8. Animage encoding method performed by an image encoding apparatus, themethod comprising: determining a partitioning method of a current blockas one of a first partitioning method and a second partitioning methodbased on slice information of a slice to which the current block belongsand information on partitioning of the current block; obtaining a codingblock by partitioning the current block using the partitioning method;obtaining prediction information of the coding block; and encoding theprediction information of the coding block, wherein, when thepartitioning method of the current block is determined to the firstpartitioning method, a luma block and a chroma block corresponding tothe current block are partitioned by a same partitioning structure,wherein, when the partitioning method of the current block is determinedto the second partitioning method, and a size of the current block islarger than a predetermined threshold value, the luma block and thechroma block corresponding to the current block are partitioned by asame partitioning structure, and wherein, when the partitioning methodof the current block is determined to the second partitioning method,and the size of the current block is less than or equal to thepredetermined threshold value, the luma block and the chroma blockcorresponding to the current block are partitioned by a differentpartitioning structure from each other.
 9. The image encoding method ofclaim 8, wherein the slice information is a slice type of the slice towhich the current block belongs.
 10. The image encoding method of claim9, wherein the determining the partitioning method of the current blockcomprises determining whether a slice type of the slice to which thecurrent block belongs is I slice or not.
 11. The image encoding methodof claim 8, wherein the information on partitioning of the current blockis signaled in a sequence parameter set (SPS).
 12. The image encodingmethod of claim 8, wherein the information on partitioning of thecurrent block is a flag information.
 13. The image encoding method ofclaim 8, wherein the predetermined threshold value is
 64. 14. A recodingmedium storing a bitstream formed by a method for encoding a videosignal, the method comprising: determining a partitioning method of acurrent block as one of a first partitioning method and a secondpartitioning method based on slice information of a slice to which thecurrent block belongs and information on partitioning of the currentblock; obtaining a coding block by partitioning the current block usingthe partitioning method; and obtaining prediction information of thecoding block; and encoding the prediction information of the codingblock, wherein, when the partitioning method of the current block isdetermined to the first partitioning method, a luma block and a chromablock corresponding to the current block are partitioned by a samepartitioning structure, wherein, when the partitioning method of thecurrent block is determined to the second partitioning method, and asize of the current block is larger than a predetermined thresholdvalue, the luma block and the chroma block corresponding to the currentblock are partitioned by a same partitioning structure, and wherein,when the partitioning method of the current block is determined to thesecond partitioning method, and the size of the current block is lessthan or equal to the predetermined threshold value, the luma block andthe chroma block corresponding to the current block are partitioned by adifferent partitioning structure from each other.